diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,10 @@
 
 For a full list of changes, see the history on [GitHub](https://github.com/hapytex/css-selectors).
 
+## Version 0.5.0.0
+
+Added pseudo-elements and pseudo-classes. The `Binary` instances are updated and *not* backedwards compatible.
+
 ## Version 0.4.0.0
 
 All css items are now a member of the `Generic` and the `Hashable` typeclass.
diff --git a/README.md b/README.md
--- a/README.md
+++ b/README.md
@@ -10,10 +10,8 @@
 It has a *quasiquoter* to enable Haskell to validate the css selector at compile
 time.
 
-Currently the css grammar is implemented *without* the pseudo-classes,
-pseudo-elements and negations. One can furthermore calculate the specificity of
-a css-selector, and thus perform an analysis over what css-selector will take
-precedence.
+One can furthermore calculate the specificity of a css-selector, and thus
+perform an analysis over what css-selector will take precedence.
 
 The package documentation can be found on the [GitHub pages](https://hapytex.github.io/css-selectors/).
 
@@ -25,24 +23,39 @@
      *comma-separated*;
   2. A `Selector` is a custom linked list implementation where the "cons" (the
      `Combined` data constructor) contains a besides a reference to a
-     `SelectorSequence` (head) and a `Selector` (tail), it specifies what
-     `SelectorCombinator` is used. A `Selector` has at least one
-     `SelectorSequence`, this is constructoed with the `Selector` data
+     `PseudoSelectorSequence` (head) and a `Selector` (tail), it specifies what
+     `PseudoSelectorCombinator` is used. A `Selector` has at least one
+     `PseudoSelectorSequence`, this is constructoed with the `Selector` data
      constructor;
-  3. A `SelectorSequence` contains a `TypeSelector` (in case the `TypeSelector`
+  3. A `PseudoSelectorSequence` is a `Selector` sequence with an *optional* `PseudoElement`, that
+     pseudo element is written at the end of the `PseudoSelectorSequence` when specified in the CSS
+     selector;
+  4. A `SelectorSequence` contains a `TypeSelector` (in case the `TypeSelector`
      is `Universal`, this does not need to be part of the css-selector
      expression); and a set of zero or more `SelectorFilter`s;
-  4. A `SelectorFilter` is a `Hash`, a `Class`, or an `Attrib`;
-  5. Both a `TypeSelector` and an `AttributeName` have a namespace. A namespace
+  5. A `SelectorFilter` is a `Hash`, a `Class`, `Attrib`, `PseudoClass`, or a `Negation`;
+  6. Both a `TypeSelector` and an `AttributeName` have a namespace. A namespace
      can be any (`*`), empty, or a namespace (which should be a valid
      identifier);
-  6. A `Hash` is a valid identifier prepended with a number sign (`#`);
-  7. A `Class` is a valid identifier prepended with a dot (`.`);
-  8. An `Attribute` can be an `Exist` object that imposes a constraint that the
+  7. A `Hash` is a valid identifier prepended with a number sign (`#`);
+  8. A `Class` is a valid identifier prepended with a dot (`.`);
+  9. An `Attribute` can be an `Exist` object that imposes a constraint that the
      attribute should exist for the given tag, or an `Attrib` that specifies
      that the attribute exists, and that the value for this attribute satisfies
      a given constraint. This constraint is determined by the
-     `AttributeCombinator` and the value of the `Attrib` object.
+     `AttributeCombinator` and the value of the `Attrib` object;
+  10. A `Negation` is written in a css selector with `:not(…)`. It can contain a `TypeSelector`, `Hash`,
+      `Class` or `PseudoClass`, it can *not* contain a nested `:not(…)`.
+  11. A `PseudoClass` is an identifier after a single colon (`:`). Some pseudo classes
+     are functions that are then called with a parameter. For the `:nth-child(…)`, `:nth-last-child(…)`,
+     `:nth-last-of-type(…)`, and `:nth-of-type(…)` these functions take an `Nth` as parameter. This
+     parameter specifies which childs will be selected. The `:lang(…)` pseudo class
+     takes the name of a language, for example `en-US`;
+  12. An `Nth` describes what childs are selected, for example `4n+2`, this is used as a function
+      parameter for the `NthChild`, `NthLastChild`, `NthLastOfType` and `NthOfType` pseudo classes; and
+  13. A `PseudoElement` is an optional item at the end of a `SelectorSequence`. Usually pseudo elements are
+      written with two colons in front, for example `::before` and `::after`. For backwards compatibility,
+      these can also be written as `:before` and `:after`.
 
 ## Quasiquoter
 
diff --git a/css-selectors.cabal b/css-selectors.cabal
--- a/css-selectors.cabal
+++ b/css-selectors.cabal
@@ -1,5 +1,5 @@
 name:                css-selectors
-version:             0.4.0.3
+version:             0.5.0.0
 synopsis:            Parsing, rendering and manipulating css selectors in Haskell.
 description:
   A library for parsing, manipulating, and rendering css selectors (not css files,
@@ -46,8 +46,9 @@
     , binary >=0.2
     , blaze-markup >=0.8
     , bytestring >=0.9
-    , data-default >=0.7
+    , data-default-class >=0.0.1
     , Decimal >=0.4.2
+    , deepseq >=1.4.3.0
     , hashable >=1.2.7.0
     , QuickCheck >=2.8
     , shakespeare >=2.0
diff --git a/src/Css3/Selector/Core.hs b/src/Css3/Selector/Core.hs
--- a/src/Css3/Selector/Core.hs
+++ b/src/Css3/Selector/Core.hs
@@ -1,4 +1,4 @@
-{-# LANGUAGE CPP, DeriveDataTypeable, DeriveGeneric, OverloadedStrings, PatternSynonyms, TemplateHaskellQuotes, TypeFamilies #-}
+{-# LANGUAGE CPP, DeriveDataTypeable, DeriveGeneric, FlexibleInstances, OverloadedStrings, PatternSynonyms, TemplateHaskellQuotes, TypeFamilies #-}
 
 {-|
 Module      : Css3.Selector.Core
@@ -11,15 +11,21 @@
 -}
 module Css3.Selector.Core (
     -- * ToCssSelector typeclass
-    ToCssSelector(..)
+    ToCssSelector(toCssSelector, toSelectorGroup, specificity', toPattern, normalize)
     -- * Selectors and combinators
     , Selector(..)
     , SelectorCombinator(..), SelectorGroup(..)
+    , PseudoElement(After, Before, FirstLetter, FirstLine, Marker, Placeholder, Selection), PseudoSelectorSequence(Sequence, (:.::)), (.::)
+    , PseudoClass(
+          Active, Checked, Default, Disabled, Empty, Enabled, Focus, Fullscreen, Hover, Indeterminate, InRange, Invalid, Lang
+        , Link, NthChild, NthLastChild, NthLastOfType, NthOfType, OnlyOfType, OnlyChild, Optional, OutOfRange, ReadOnly
+        , ReadWrite, Required, Root, Target, Valid, Visited
+        ), (.:), pattern FirstChild, pattern FirstOfType, pattern LastChild, pattern LastOfType, Language
     , SelectorSequence(..)
     , combinatorText, combine
     , (.>), (.+), (.~)
     -- * Filters
-    , SelectorFilter(..), filters, filters', addFilters, (.:)
+    , SelectorFilter(SHash, SClass, SAttrib, SPseudo, SNot), filters, filters', addFilters, (.@)
     -- * Namespaces
     , Namespace(..), pattern NEmpty
     -- * Type selectors
@@ -32,6 +38,10 @@
     , Class(..), (...)
     -- * Hashes
     , Hash(..), (.#)
+    -- * Negation
+    , Negation(NTypeSelector, NHash, NClass, NAttrib, NPseudo, NPseudoElement)
+    -- * Nth items
+    , Nth(Nth, linear, constant), pattern Even, pattern Odd, pattern One, nthValues, nthIsEmpty, nthValues0, nthValues1, normalizeNth, nthContainsValue
     -- * Specificity
     , SelectorSpecificity(..), specificity, specificityValue
     -- * Read and write binary content
@@ -43,14 +53,16 @@
 import Codec.Compression.GZip(CompressParams, compress, compressWith, decompress)
 
 import Control.Applicative(liftA2)
+import Control.DeepSeq(NFData)
 
 import Css3.Selector.Utils(encodeIdentifier, encodeText, toIdentifier)
 
 import Data.Aeson(Value(String), ToJSON(toJSON))
 import Data.Binary(Binary(put, get), Get, Put, decode, encode, getWord8, putWord8)
 import Data.ByteString.Lazy(ByteString)
+import Data.Char(toLower)
 import Data.Data(Data)
-import Data.Default(Default(def))
+import Data.Default.Class(Default(def))
 import Data.Function(on)
 import Data.Hashable(Hashable)
 import Data.List(sort, unfoldr)
@@ -62,22 +74,22 @@
 #endif
 import Data.String(IsString(fromString))
 import qualified Data.Text as T
-import Data.Text(Text, cons, inits, intercalate, pack, tails, unpack)
+import Data.Text(Text, cons, inits, intercalate, pack, snoc, tails, unpack)
 
 import GHC.Exts(IsList(Item, fromList, toList))
 import GHC.Generics(Generic)
 
 import Language.Haskell.TH.Lib(appE, conE)
 #if MIN_VERSION_template_haskell(2,17,0)
-import Language.Haskell.TH.Syntax(Lift(lift, liftTyped), Exp(AppE, ConE, LitE), Lit(StringL), Name, Pat(ConP, ListP, ViewP), Q, unsafeCodeCoerce)
+import Language.Haskell.TH.Syntax(Lift(lift, liftTyped), Quote, Exp(AppE, ConE, LitE), Lit(IntegerL, StringL), Name, Pat(ConP, ListP, LitP, ViewP), unsafeCodeCoerce)
 #elif MIN_VERSION_template_haskell(2,16,0)
-import Language.Haskell.TH.Syntax(Lift(lift, liftTyped), Exp(AppE, ConE, LitE), Lit(StringL), Name, Pat(ConP, ListP, ViewP), Q, unsafeTExpCoerce)
+import Language.Haskell.TH.Syntax(Lift(lift, liftTyped), Exp(AppE, ConE, LitE), Lit(IntegerL, StringL), Name, Pat(ConP, ListP, LitP, ViewP), Q, unsafeTExpCoerce)
 #else
-import Language.Haskell.TH.Syntax(Lift(lift), Exp(AppE, ConE, LitE), Lit(StringL), Name, Pat(ConP, ListP, ViewP), Q)
+import Language.Haskell.TH.Syntax(Lift(lift), Exp(AppE, ConE, LitE), Lit(IntegerL, StringL), Name, Pat(ConP, ListP, LitP, ViewP), Q)
 #endif
 
 import Test.QuickCheck.Arbitrary(Arbitrary(arbitrary, shrink), arbitraryBoundedEnum)
-import Test.QuickCheck.Gen(Gen, frequency, listOf, listOf1, oneof)
+import Test.QuickCheck.Gen(Gen, elements, frequency, listOf, listOf1, oneof)
 
 import Text.Blaze(ToMarkup(toMarkup), text)
 import Text.Blaze.Internal(Markup)
@@ -94,11 +106,101 @@
 
 instance Hashable SelectorSpecificity
 
+instance NFData SelectorSpecificity
+
 -- | Calculate the specificity value of the 'SelectorSpecificity'
 specificityValue :: SelectorSpecificity -- ^ The 'SelectorSpecificity' to calculate the specificity value from.
     -> Int  -- ^ The specificity level of the 'SelectorSpecificity'. If the value is higher, the rules in the css selector take precedence.
 specificityValue (SelectorSpecificity a b c) = 100*a + 10*b + c
 
+-- | A data type that is used to select children and elements of type with the @:nth-child@, @:nth-last-child@, @:nth-last-of-type@ and @:nth-of-type@.
+-- if the 'One' is used as argument, then the pseudo classes are @:first-child@, @:first-of-type@, @:last-child@, and @:last-of-type@.
+data Nth
+  = Nth {
+    linear :: Int  -- ^ The linear part of the 'Nth' object: the integral number before the @n@.
+  , constant :: Int  -- ^ The constant part of the 'Nth' object.
+  } deriving (Data, Eq, Generic, Ord, Read, Show)
+
+instance Hashable Nth
+
+instance NFData Nth
+
+-- | Check if the given 'Nth' object contains /no/ items.
+nthIsEmpty
+  :: Nth  -- ^ The given 'Nth' object object to check.
+  -> Bool  -- ^ 'True' if the given 'Nth' object does /not/ contain any items; 'False' otherwise.
+nthIsEmpty (Nth n c) = n <= 0 && c <= 0
+
+-- | Normalize the given 'Nth' object to a normalized one. If and only if the
+-- normalized variants are the same of two 'Nth' objects, then these will produce
+-- the same list of values. Normalization is idempotent: calling 'normalizeNth'
+-- on a normalized 'Nth' will produce the same 'Nth'.
+normalizeNth
+  :: Nth -- ^ The given 'Nth' item to normalize.
+  -> Nth -- ^ The normalized variant of the given 'Nth' object.
+normalizeNth nth@(Nth n c)
+  | n <= 0 && c + n <= 0 = Nth 0 (max 0 c)
+  | n > 0 && c < 0 = let cn = c `mod` n in if cn /= 0 then Nth n cn else Nth n n
+  | n > 0 && c == 0 = Nth n n
+  | otherwise = nth
+
+-- | Obtain the one-based indices that match the given 'Nth' object. The CSS3 selectors
+-- are one-based: the first child has index 1.
+nthValues
+  :: Nth  -- The 'Nth' object that specifies the given range.
+  -> [Int]  -- ^ A list of one-based indexes that contain the items selected by the 'Nth' object. The list can be infinite.
+nthValues (Nth n c)
+  | n > 0 && c <= 0 = let {c' = c `mod` n; cn' = c' + n} in (if c' /= 0 then (c':) else id) [cn', cn' + n ..]
+  | n > 0 = [c, c+n ..]
+  | n < 0 = [ c, c+n .. 1 ]
+  | otherwise = [c | c > 0]
+
+-- | Check if the given 'Nth' object contains a given value.
+nthContainsValue
+  :: Nth -- ^ The given 'Nth' object that specifies a sequence.
+  -> Int  -- ^ The given index for which we check if it is contained in the given 'Nth' object.
+  -> Bool  -- ^ This function returns 'True' if the given item is a member of the given 'Nth' sequence; 'False' otherwise.
+nthContainsValue (Nth 0 c) i = c == i && i > 0
+nthContainsValue (Nth n c) i = i > 0 && (i - c) `div` n >= 0 && (i - c) `mod` n == 0
+
+-- | Obtain the one-based indices that match the given 'Nth' object. The CSS3 selectors
+-- are one-based: the first child has index 1. This is an alias of the 'nthValues' function.
+nthValues1
+  :: Nth  -- The 'Nth' object that specifies the given range.
+  -> [Int]  -- ^ A list of zero-based indexes that contain the items selected by the 'Nth' object. The list can be infinite.
+nthValues1 = nthValues
+
+-- | Obtain the zero-based indices that match the given 'Nth' object. One can use this for list/vector processing since
+-- the CSS3 selectors start with index 1. The 'nthValues1' can be used for one-based indexes.
+nthValues0
+  :: Nth  -- The 'Nth' object that specifies the given range.
+  -> [Int]  -- ^ A list of zero-based indexes that contain the items selected by the 'Nth' object. The list can be infinite.
+nthValues0 = map (subtract 1) . nthValues
+
+-- | A pattern synonym that is used in CSS to specify a sequence that starts with two and each time increases with two.
+pattern Even :: Nth
+pattern Even = Nth 2 0
+
+-- | A pattern synonym that is used in CSS to specify a sequence that starts with one and each time increases with two.
+pattern Odd :: Nth
+pattern Odd = Nth 2 1
+
+-- | An 'Nth' item that spans a collection with only @1@ as value. This is used to transform @:nth-child@ to @:first-child@ for example.
+pattern One :: Nth
+pattern One = Nth 0 1
+
+-- | Convert the given 'Nth' object to text used by the CSS selector.
+nthToText
+  :: Nth  -- ^ The 'Nth' object for which we determine the textual presentation.
+  -> Text -- ^ The textual presentation of the 'Nth' object in a CSS selector.
+nthToText Even = "even"
+nthToText Odd = "odd"
+nthToText (Nth n 0) = snoc (pack (show n)) 'n'
+nthToText (Nth 0 b) = pack (show b)
+nthToText (Nth n b)
+  | b <= 0 = pack (show n ++ 'n' : show b)
+  | otherwise = pack (show n ++ 'n' : '+' : show b)
+
 -- | A class that defines that the given type can be converted to a css selector
 -- value, and has a certain specificity.
 class ToCssSelector a where
@@ -169,15 +271,18 @@
 
 instance Hashable SelectorGroup
 
+instance NFData SelectorGroup
+
 -- | The type of a single selector. This is a sequence of 'SelectorSequence's that
 -- are combined with a 'SelectorCombinator'.
 data Selector =
-      Selector SelectorSequence -- ^ Convert a given 'SelectorSequence' to a 'Selector'.
-    | Combined SelectorSequence SelectorCombinator Selector -- ^ Create a combined selector where we have a 'SelectorSequence' that is combined with a given 'SelectorCombinator' to a 'Selector'.
+      Selector PseudoSelectorSequence -- ^ Convert a given 'SelectorSequence' to a 'Selector'.
+    | Combined PseudoSelectorSequence SelectorCombinator Selector -- ^ Create a combined selector where we have a 'SelectorSequence' that is combined with a given 'SelectorCombinator' to a 'Selector'.
     deriving (Data, Eq, Generic, Ord, Show)
 
 instance Hashable Selector
 
+instance NFData Selector
 
 -- | A type that contains the possible ways to combine 'SelectorSequence's.
 data SelectorCombinator =
@@ -189,6 +294,8 @@
 
 instance Hashable SelectorCombinator
 
+instance NFData SelectorCombinator
+
 -- | Convert the 'SelectorCombinator' to the equivalent css selector text. A
 -- space for 'Descendant', a @>@ for 'Child', a @+@ for 'DirectlyPreceded', and
 -- a @~@ for 'Preceded'
@@ -236,6 +343,27 @@
 
 instance Hashable SelectorSequence
 
+instance NFData SelectorSequence
+
+-- | A 'SelectorSequence' with an optional 'PseudoElement' at the end. Each /element/ of a 'Selector' can
+-- have /at most/ one 'PseudoElement'.
+data PseudoSelectorSequence
+    = Sequence SelectorSequence  -- ^ A data constructor where there is no optional 'PseudoElement' involved.
+    | SelectorSequence :.:: PseudoElement  -- ^ A data constructor for a 'SelectorSequence' with a 'PseudoElement'.
+    deriving (Data, Eq, Generic, Ord, Show)
+
+instance Hashable PseudoSelectorSequence
+
+instance NFData PseudoSelectorSequence
+
+-- | Add a given 'PseudoElement' to the given 'SelectorSequence' to produce a 'PseudoSelectorSequence'. Since
+-- a 'PseudoElement' is an instance of 'IsString', this can thus be used to combine string literals.
+(.::)
+  :: SelectorSequence  -- ^ The given 'SelectorSequence' to which we add the pseudo element.
+  -> PseudoElement  -- ^ The given 'PseudoElement' to add to the 'SelectorSequence'.
+  -> PseudoSelectorSequence  -- ^ The corresponding 'PseudoSelectorSequence'.
+(.::) = (:.::)
+
 -- | Add a given list of 'SelectorFilter's to the given 'SelectorSequence'. The
 -- filters are applied left-to-right.
 addFilters :: SelectorSequence -- ^ The 'SelectorSequence' to apply the filter on.
@@ -244,10 +372,10 @@
 addFilters = foldl Filter
 
 -- | An infix variant of the 'addFilters' function.
-(.:) :: SelectorSequence -- ^ The 'SelectorSequence' to apply the filter on.
+(.@) :: SelectorSequence -- ^ The 'SelectorSequence' to apply the filter on.
     -> [SelectorFilter] -- ^ The list of 'SelectorFilter's to apply on the 'SelectorSequence'.
     -> SelectorSequence -- ^ A modified 'SelectorSequence' where we applied the list of 'SelectorFilter's.
-(.:) = addFilters
+(.@) = addFilters
 
 -- | Obtain the list of filters that are applied in the given 'SelectorSequence'
 -- in /reversed/ order.
@@ -265,14 +393,34 @@
 
 -- | A type that sums up the different ways to filter a type selector: with an
 -- id (hash), a class, and an attribute.
-data SelectorFilter =
-      SHash Hash -- ^ A 'Hash' object as filter.
+data SelectorFilter
+    = SHash Hash -- ^ A 'Hash' object as filter.
     | SClass Class -- ^ A 'Class' object as filter.
     | SAttrib Attrib -- ^ An 'Attrib' object as filter.
+    | SPseudo PseudoClass -- ^ A 'PseudoClass' object as filter.
+    | SNot Negation  -- ^ A @:not(…)@ clause that contains a simple selector to negate.
     deriving (Data, Eq, Generic, Ord, Show)
 
 instance Hashable SelectorFilter
 
+instance NFData SelectorFilter
+
+-- | A data type that contains all possible items that can be used in a @:not(…)@ clause.
+-- Since a @:not(…)@ cannot be nested in another @:not(…)@, we see an 'SNot' as a special
+-- case, and not as a 'PseudoClass'.
+data Negation
+    = NTypeSelector TypeSelector  -- ^ A 'TypeSelector' for the @:not(…)@ clause.
+    | NHash Hash  -- ^ A 'Hash' for the @:not(…)@ clause.
+    | NClass Class  -- ^ A 'Class' for the @:not(…)@ clause.
+    | NAttrib Attrib  -- ^ An 'Attrib' for the @:not(…)@ clause.
+    | NPseudo PseudoClass  -- ^ A 'PseudoClass' for the @:not(…)@ clause.
+    | NPseudoElement PseudoElement  -- ^ A 'PseudoElement' for the @:not(…)@ clause.
+    deriving (Data, Eq, Generic, Ord, Show)
+
+instance Hashable Negation
+
+instance NFData Negation
+
 -- | A css attribute can come in two flavors: either a constraint that the
 -- attribute should exists, or a constraint that a certain attribute should have
 -- a certain value (prefix, suffix, etc.).
@@ -283,6 +431,8 @@
 
 instance Hashable Attrib
 
+instance NFData Attrib
+
 -- | A flipped version of the 'Attrib' data constructor, where one first
 -- specifies the conbinator, then the 'AttributeName' and finally the value.
 attrib :: AttributeCombinator -- ^ The 'AttributeCombinator' that specifies the required relation between the attribute and a value.
@@ -353,6 +503,12 @@
     -> TypeSelector -- ^ A 'TypeSelector' object constructed with the 'Namespace' and 'ElementName'.
 (.|) = TypeSelector
 
+-- | Filter a given 'SelectorSequence' with a given 'PseudoClass'.
+(.:) :: SelectorSequence -- ^ The given 'SelectorSequence' to filter.
+    -> PseudoClass -- ^ The given 'PseudoClass' to filter the 'SelectorSequence' further.
+    -> SelectorSequence -- ^ A 'SelectorSequence' that is filtered additionally with the given 'PseudoClass'.
+(.:) = (. SPseudo) . Filter
+
 -- | The namespace of a css selector tag. The namespace can be 'NAny' (all
 -- possible namespaces), or a namespace with a given text (this text can be
 -- empty).
@@ -363,6 +519,8 @@
 
 instance Hashable Namespace
 
+instance NFData Namespace
+
 -- | The empty namespace. This is /not/ the wildcard namespace (@*@). This is a
 -- bidirectional namespace and can thus be used in expressions as well.
 pattern NEmpty :: Namespace
@@ -377,6 +535,8 @@
 
 instance Hashable ElementName
 
+instance NFData ElementName
+
 -- | A typeselector is a combination of a selector for a namespace, and a
 -- selector for an element name. One, or both can be a wildcard.
 data TypeSelector = TypeSelector {
@@ -386,6 +546,8 @@
 
 instance Hashable TypeSelector
 
+instance NFData TypeSelector
+
 -- | An attribute name is a name that optionally has a namespace, and the name
 -- of the attribute.
 data AttributeName = AttributeName {
@@ -395,9 +557,14 @@
 
 instance Hashable AttributeName
 
+instance NFData AttributeName
+
 -- | We use 'Text' as the type to store an attribute value.
 type AttributeValue = Text
 
+-- | We use 'Text' to specify the language in the @:lang(…)@ pseudo class.
+type Language = Text
+
 -- | The possible ways to match an attribute with a given value in a css
 -- selector.
 data AttributeCombinator =
@@ -411,6 +578,87 @@
 
 instance Hashable AttributeCombinator
 
+instance NFData AttributeCombinator
+
+-- | A data type that contains the possible pseudo classes. In a CSS selector
+-- the pseudo classes are specified with a single colon, for example @:active@.
+-- These filter on the /state/ of the items. A full list of pseudo classes
+-- is available <https://www.w3schools.com/css/css_pseudo_classes.asp here>.
+data PseudoClass
+  = Active  -- ^ The @:active@ pseudo class.
+  | Checked  -- ^ The @:checked@ pseudo class.
+  | Default  -- ^ The @:default@ pseudo class.
+  | Disabled  -- ^ The @:disabled@ pseudo class.
+  | Empty  -- ^ The @:empty@ pseudo class.
+  | Enabled  -- ^ The @:enabled@ pseudo class.
+  | Focus  -- ^ The @:focus@ pseudo class.
+  | Fullscreen  -- ^ The @:fullscreen@ pseudo class.
+  | Hover  -- ^ The @:hover@ pseudo class.
+  | Indeterminate  -- ^ The @:indeterminate@ pseudo class.
+  | InRange  -- ^ The @:in-range@ pseudo class.
+  | Invalid  -- ^ The @:invalid@ pseudo class.
+  | Lang Language  -- ^ The @:lang(…)@ pseudo class, the language parameter is at the moment a 'Text' object, but only uppercase, lowercase and hyphens are characters that can be parsed.
+  | Link  -- ^ The @:link@ pseudo class.
+  | NthChild Nth  -- ^ The @:nth-child(…)@ pseudo class, if the 'Nth' parameter is 'One', then it is equivalent to @:first-child@.
+  | NthLastChild Nth  -- ^ The @:nth-last-child(…)@ pseudo class, if the 'Nth' parameter is 'One', then it is equivalent to @:last-child@.
+  | NthLastOfType Nth  -- ^ The @:nth-last-of-type(…)@ pseudo class, if the 'Nth' parameter is 'One', then it is equivalent to @:last-of-type@.
+  | NthOfType Nth  -- ^ The @:nth-of-type(…)@ pseudo class, if the 'Nth' parameter is 'One', then it is equivalent to @:first-of-type@.
+  | OnlyOfType  -- ^ The @:only-of-type@ pseudo class.
+  | OnlyChild  -- ^ The @:only-child@ pseudo class.
+  | Optional  -- ^ The @:optional@ pseudo class.
+  | OutOfRange  -- ^ The @:out-of-range@ pseudo class.
+  | ReadOnly  -- ^ The @:read-only@ pseudo class.
+  | ReadWrite  -- ^ The @:rad-write@ pseudo class.
+  | Required  -- ^ The @:required@ pseudo class.
+  | Root  -- ^ The @:root@ pseudo class.
+  | Target  -- ^ The @:target@ pseudo class.
+  | Valid  -- ^ The @:valid@ pseudo class.
+  | Visited  -- ^ The @:visited@ pseudo class.
+  deriving (Data, Eq, Generic, Ord, Read, Show)
+
+instance Hashable PseudoClass
+
+instance NFData PseudoClass
+
+-- | A pattern synonym for @:nth-child(1)@. If @NthChild (Nth 0 1)@ is used, then
+-- this will render as @:first-child@.
+pattern FirstChild :: PseudoClass
+pattern FirstChild = NthChild One
+
+-- | A pattern synonym for @:nth-of-type(1)@. If @NthOfType (Nth 0 1)@ is used, then
+-- this will render as @:first-of-type@.
+pattern FirstOfType :: PseudoClass
+pattern FirstOfType = NthOfType One
+
+-- | A pattern synonym for @:nth-last-child(1)@. If @NthLastChild (Nth 0 1)@ is used, then
+-- this will render as @:last-child@.
+pattern LastChild :: PseudoClass
+pattern LastChild = NthLastChild One
+
+-- | A pattern synonym for @:nth-last-of-type(1)@. If @NthLastOfType (Nth 0 1)@ is used, then
+-- this will render as @:last-of-type@.
+pattern LastOfType :: PseudoClass
+pattern LastOfType = NthLastOfType One
+
+-- | An enum type that contains the possible /pseudo elements/. A pseudo
+-- element is specified by two colon characters (@::@), followed by the name of
+-- the pseudo element. The 'After', 'Before', 'FirstLine' and 'FirstLetter'
+-- can be written with a single colon for backwards compatibility with
+-- CSS 1 and CSS 2.
+data PseudoElement
+  = After  -- ^ The @::after@ pseudo-elements can be used to describe generated content after an element’s content.
+  | Before  -- ^ The @::before@ pseudo-element can be used to describe generated content before an element’s content.
+  | FirstLetter  -- ^ The @::first-line@ pseudo-element describes the contents of the first formatted line of an element.
+  | FirstLine  -- ^ The @::first-letter@ pseudo-element represents the first letter of an element, if it is not preceded by any other content (such as images or inline tables) on its line.
+  | Marker -- ^ The @::marker@ pseudo-element selects the markers of list items.
+  | Placeholder -- ^ The @::placeholder@ pseudo-element selects form elements with placeholder text, and let you style the placeholder text.
+  | Selection -- ^ The @::selection@ pseudo-element matches the portion of an element that is selected by a user.
+  deriving (Bounded, Data, Enum, Eq, Generic, Ord, Read, Show)
+
+instance Hashable PseudoElement
+
+instance NFData PseudoElement
+
 -- | A css class, this is wrapped in a data type. The type only wraps the class
 -- name, not the dot prefix.
 newtype Class = Class {
@@ -419,6 +667,8 @@
 
 instance Hashable Class
 
+instance NFData Class
+
 -- | A css hash (used to match an element with a given id). The type only wraps
 -- the hash name, not the hash (@#@) prefix.
 newtype Hash = Hash {
@@ -427,6 +677,8 @@
 
 instance Hashable Hash
 
+instance NFData Hash
+
 -- | Convert the given 'AttributeCombinator' to its css selector counterpart.
 attributeCombinatorText :: AttributeCombinator -- ^ The 'AttributeCombinator' for which we obtain the corresponding css selector text.
     -> AttributeValue -- ^ The css selector text for the given 'AttributeCombinator'.
@@ -498,6 +750,59 @@
 instance IsString Attrib where
     fromString = Exist . fromString
 
+instance IsString PseudoClass where
+    fromString = go . map toLower
+      where go "active" = Active
+            go "checked" = Checked
+            go "default" = Default
+            go "disabled" = Disabled
+            go "empty" = Empty
+            go "enabled" = Enabled
+            go "first-child" = FirstChild
+            go "first-of-type" = FirstOfType
+            go "focus" = Focus
+            go "fullscreen" = Fullscreen
+            go "hover" = Hover
+            go "indeterminate" = Indeterminate
+            go "in-range" = InRange
+            go "invalid" = Invalid
+            go "last-child" = LastChild
+            go "last-of-type" = LastOfType
+            go "link" = Link
+            --  items with :lang(...) and :...(nth)
+            go "only-of-type" = OnlyOfType
+            go "only-child" = OnlyChild
+            go "optional" = Optional
+            go "out-of-range" = OutOfRange
+            go "read-only"= ReadOnly
+            go "read-write" = ReadWrite
+            go "required" = Required
+            go "root" = Root
+            go "target" = Target
+            go "valid" = Valid
+            go "visited" = Visited
+            go x = error ("The pseudo class \"" ++ x ++ "\" is not a valid pseudo class.")
+
+instance IsString ((->) Nth PseudoClass) where
+  fromString = go . map toLower
+    where go "nth-child" = NthChild
+          go "nth-last-child" = NthLastChild
+          go "nth-last-of-type" = NthLastOfType
+          go "nth-of-type" = NthLastOfType
+          go x = error ("There is no pseudo class \"" ++ x ++ "\" that takes an Nth object as parameter.")
+
+instance IsString PseudoElement where
+    fromString = go . map toLower
+      where go "after" = After
+            go "before" = Before
+            go "first-letter" = FirstLetter
+            go "first-line" = FirstLine
+            go "marker" = Marker
+            go "placeholder" = Placeholder
+            go "selection" = Selection
+            go x = error ("The pseudo element \"" ++ x ++ "\" is not a valid pseudo element.")
+
+
 -- IsList instances
 instance IsList SelectorGroup where
     type Item SelectorGroup = Selector
@@ -509,29 +814,41 @@
 _textToPattern t = ViewP (AppE (ConE '(==)) (AppE (ConE 'pack) (LitE (StringL (unpack t))))) (_constantP 'True)
 
 _constantP :: Name -> Pat
-_constantP = flip ConP []
+#if MIN_VERSION_template_haskell(2,18,0)
+_constantP = flip (`ConP` []) []
+#else
+_constantP = (`ConP` [])
+#endif
 
+_conP :: Name -> [Pat] -> Pat
+#if MIN_VERSION_template_haskell(2,18,0)
+_conP = (`ConP` [])
+#else
+_conP = ConP
+#endif
+
+
 instance ToCssSelector SelectorGroup where
     toCssSelector (SelectorGroup g) = intercalate " , " (map toCssSelector (toList g))
     toSelectorGroup = id
     specificity' (SelectorGroup g) = foldMap specificity' g
-    toPattern (SelectorGroup g) = ConP 'SelectorGroup [go g]
-        where go (x :| xs) = ConP '(:|) [toPattern x, ListP (map toPattern xs)]
+    toPattern (SelectorGroup g) = _conP 'SelectorGroup [go g]
+        where go (x :| xs) = _conP '(:|) [toPattern x, ListP (map toPattern xs)]
     normalize (SelectorGroup g) = SelectorGroup (Data.List.NonEmpty.sort (normalize <$> g))
 
 instance ToCssSelector Class where
     toCssSelector = cons '.' . encodeIdentifier . unClass
     toSelectorGroup = toSelectorGroup . SClass
     specificity' = const (SelectorSpecificity 0 1 0)
-    toPattern (Class c) = ConP 'Class [_textToPattern c]
+    toPattern (Class c) = _conP 'Class [_textToPattern c]
 
 instance ToCssSelector Attrib where
     toCssSelector (Exist name) = "[" <> toCssSelector name <> "]"
     toCssSelector (Attrib name op val) = "[" <> toCssSelector name <> attributeCombinatorText op <> encodeText '"' val <> "]"
     toSelectorGroup = toSelectorGroup . SAttrib
     specificity' = const (SelectorSpecificity 0 1 0)
-    toPattern (Exist name) = ConP 'Exist [toPattern name]
-    toPattern (Attrib name op val) = ConP 'Attrib [toPattern name, _constantP (go op), _textToPattern val]
+    toPattern (Exist name) = _conP 'Exist [toPattern name]
+    toPattern (Attrib name op val) = _conP 'Attrib [toPattern name, _constantP (go op), _textToPattern val]
         where go Exact = 'Exact
               go Include = 'Include
               go DashMatch = 'DashMatch
@@ -544,13 +861,13 @@
     toCssSelector (AttributeName n e) = toCssSelector n <> "|" <> encodeIdentifier e
     toSelectorGroup = toSelectorGroup . Exist
     specificity' = mempty
-    toPattern (AttributeName n a) = ConP 'AttributeName [toPattern n, _textToPattern a]
+    toPattern (AttributeName n a) = _conP 'AttributeName [toPattern n, _textToPattern a]
 
 instance ToCssSelector Hash where
     toCssSelector = cons '#' . encodeIdentifier . unHash
     toSelectorGroup = toSelectorGroup . SHash
     specificity' = const (SelectorSpecificity 1 0 0)
-    toPattern (Hash h) = ConP 'Hash [_textToPattern h]
+    toPattern (Hash h) = _conP 'Hash [_textToPattern h]
 
 instance ToCssSelector Namespace where
     toCssSelector NAny = "*"
@@ -560,16 +877,16 @@
     toPattern NAny = _constantP 'NAny
     -- used to make patterns more readable
     toPattern NEmpty = _constantP 'NEmpty
-    toPattern (Namespace t) = ConP 'Namespace [_textToPattern t]
+    toPattern (Namespace t) = _conP 'Namespace [_textToPattern t]
 
 instance ToCssSelector SelectorSequence where
     toCssSelector (SimpleSelector s) = toCssSelector s
     toCssSelector (Filter s f) = toCssSelector s <> toCssSelector f
-    toSelectorGroup = toSelectorGroup . Selector
+    toSelectorGroup = toSelectorGroup . Sequence
     specificity' (SimpleSelector s) = specificity' s
     specificity' (Filter s f) = specificity' s <> specificity' f
-    toPattern (SimpleSelector s) = ConP 'SimpleSelector [toPattern s]
-    toPattern (Filter s f) = ConP 'Filter [toPattern s, toPattern f]
+    toPattern (SimpleSelector s) = _conP 'SimpleSelector [toPattern s]
+    toPattern (Filter s f) = _conP 'Filter [toPattern s, toPattern f]
     normalize = flip go []
         where go (Filter s f) = go s . (normalize f:)
               go (SimpleSelector s) = addFilters (SimpleSelector (normalize s)) . sort
@@ -581,7 +898,7 @@
     specificity' (TypeSelector _ e) = specificity' e
     -- we use Universal, to make the generated pattern more convenient to read.
     toPattern Universal = _constantP 'Universal
-    toPattern (TypeSelector n t) = ConP 'TypeSelector [toPattern n, toPattern t]
+    toPattern (TypeSelector n t) = _conP 'TypeSelector [toPattern n, toPattern t]
 
 instance ToCssSelector ElementName where
     toCssSelector EAny = "*"
@@ -590,19 +907,25 @@
     specificity' EAny = mempty
     specificity' (ElementName _) = SelectorSpecificity 0 0 1
     toPattern EAny = _constantP 'EAny
-    toPattern (ElementName e) = ConP 'ElementName [_textToPattern e]
+    toPattern (ElementName e) = _conP 'ElementName [_textToPattern e]
 
 instance ToCssSelector SelectorFilter where
     toCssSelector (SHash h) = toCssSelector h
     toCssSelector (SClass c) = toCssSelector c
     toCssSelector (SAttrib a) = toCssSelector a
+    toCssSelector (SPseudo p) = toCssSelector p
+    toCssSelector (SNot n) = toCssSelector n
     toSelectorGroup = toSelectorGroup . Filter (SimpleSelector Universal)
     specificity' (SHash h) = specificity' h
     specificity' (SClass c) = specificity' c
     specificity' (SAttrib a) = specificity' a
-    toPattern (SHash h) = ConP 'SHash [toPattern h]
-    toPattern (SClass c) = ConP 'SClass [toPattern c]
-    toPattern (SAttrib a) = ConP 'SAttrib [toPattern a]
+    specificity' (SPseudo p) = specificity' p
+    specificity' (SNot n) = specificity' n  -- Selectors inside the negation pseudo-class are counted like any other, but the negation itself does not count as a pseudo-class.
+    toPattern (SHash h) = _conP 'SHash [toPattern h]
+    toPattern (SClass c) = _conP 'SClass [toPattern c]
+    toPattern (SAttrib a) = _conP 'SAttrib [toPattern a]
+    toPattern (SPseudo p) = _conP 'SPseudo [toPattern p]
+    toPattern (SNot n) = _conP 'SNot [toPattern n]
 
 instance ToCssSelector Selector where
     toCssSelector (Selector s) = toCssSelector s
@@ -610,8 +933,8 @@
     toSelectorGroup = toSelectorGroup . SelectorGroup . pure
     specificity' (Selector s) = specificity' s
     specificity' (Combined s1 _ s2) = specificity' s1 <> specificity' s2
-    toPattern (Selector s) = ConP 'Selector [toPattern s]
-    toPattern (Combined s1 c s2) = ConP 'Combined [toPattern s1, _constantP (go c), toPattern s2]
+    toPattern (Selector s) = _conP 'Selector [toPattern s]
+    toPattern (Combined s1 c s2) = _conP 'Combined [toPattern s1, _constantP (go c), toPattern s2]
         where go Descendant = 'Descendant
               go Child = 'Child
               go DirectlyPreceded = 'DirectlyPreceded
@@ -619,6 +942,138 @@
     normalize (Selector s) = Selector (normalize s)
     normalize (Combined s1 c s2) = Combined (normalize s1) c (normalize s2)
 
+instance ToCssSelector PseudoSelectorSequence where
+    toCssSelector (Sequence ss) = toCssSelector ss
+    toCssSelector (ss :.:: pe)
+      | def == ss = toCssSelector pe
+      | otherwise = toCssSelector ss <> toCssSelector pe
+    toSelectorGroup = toSelectorGroup . Selector
+    specificity' (Sequence ss) = specificity' ss
+    specificity' (ss :.:: pe) = specificity' ss <> specificity' pe
+    toPattern (Sequence ss) = _conP 'Sequence [toPattern ss]
+    toPattern (ss :.:: pe) = _conP '(:.::) [toPattern ss, toPattern pe]
+    normalize (Sequence ss) = Sequence (normalize ss)
+    normalize (ss :.:: pe) = normalize ss :.:: normalize pe
+
+_nthToPat :: Nth -> Pat
+_nthToPat (Nth n b) = _conP 'Nth [f n, f b]
+    where f = LitP . IntegerL . fromIntegral
+
+instance ToCssSelector PseudoClass where
+    toCssSelector = cons ':' . go
+      where go Active = "active"
+            go Checked = "checked"
+            go Default = "default"
+            go Disabled = "disabled"
+            go Empty = "empty"
+            go Enabled = "enabled"
+            go Focus = "focus"
+            go Fullscreen = "fullscreen"
+            go Hover = "hover"
+            go Indeterminate = "indeterminate"
+            go InRange = "in-range"
+            go Invalid = "invalid"
+            go Link = "link"
+            go (Lang l) = "lang(" <> l <> ")"
+            go FirstChild = "first-child"
+            go (NthChild nth) = "nth-child(" <> nthToText nth <> ")"
+            go LastChild = "last-child"
+            go (NthLastChild nth) = "nth-last-child(" <> nthToText nth <> ")"
+            go LastOfType = "last-of-type"
+            go (NthLastOfType nth) = "nth-last-of-type(" <> nthToText nth <> ")"
+            go FirstOfType = "first-of-type"
+            go (NthOfType nth) = "nth-of-type(" <> nthToText nth <> ")"
+            go OnlyOfType = "only-of-type"
+            go OnlyChild = "only-child"
+            go Optional = "optional"
+            go OutOfRange = "out-of-range"
+            go ReadOnly = "read-only"
+            go ReadWrite = "read-write"
+            go Required = "required"
+            go Root = "root"
+            go Target = "target"
+            go Valid = "valid"
+            go Visited = "visited"
+
+    specificity' = const (SelectorSpecificity 0 1 0)
+    toSelectorGroup = toSelectorGroup . SPseudo
+    toPattern Active = _constantP 'Active
+    toPattern Checked = _constantP 'Checked
+    toPattern Default = _constantP 'Default
+    toPattern Disabled = _constantP 'Disabled
+    toPattern Empty = _constantP 'Empty
+    toPattern Enabled = _constantP 'Enabled
+    toPattern Focus = _constantP 'Focus
+    toPattern Fullscreen = _constantP 'Fullscreen
+    toPattern Hover = _constantP 'Hover
+    toPattern Indeterminate = _constantP 'Indeterminate
+    toPattern InRange = _constantP 'InRange
+    toPattern Invalid = _constantP 'Invalid
+    toPattern Link = _constantP 'Link
+    toPattern (Lang l) = _conP 'Lang [_textToPattern l]
+    toPattern (NthChild nth) = _conP 'NthChild [_nthToPat nth]
+    toPattern (NthLastChild nth) = _conP 'NthLastChild [_nthToPat nth]
+    toPattern (NthLastOfType nth) = _conP 'NthLastOfType [_nthToPat nth]
+    toPattern (NthOfType nth) = _conP 'NthOfType [_nthToPat nth]
+    toPattern OnlyOfType = _constantP 'OnlyOfType
+    toPattern OnlyChild = _constantP 'OnlyChild
+    toPattern Optional = _constantP 'Optional
+    toPattern OutOfRange = _constantP 'OutOfRange
+    toPattern ReadOnly = _constantP 'ReadOnly
+    toPattern ReadWrite = _constantP 'ReadWrite
+    toPattern Required = _constantP 'Required
+    toPattern Root = _constantP 'Root
+    toPattern Target = _constantP 'Target
+    toPattern Valid = _constantP 'Valid
+    toPattern Visited = _constantP 'Visited
+    normalize (NthChild nth) = NthChild (normalizeNth nth)
+    normalize (NthLastChild nth) = NthLastChild (normalizeNth nth)
+    normalize (NthLastOfType nth) = NthLastOfType (normalizeNth nth)
+    normalize (NthOfType nth) = NthOfType (normalizeNth nth)
+    normalize pc = pc
+
+instance ToCssSelector Negation where
+    toCssSelector n = ":not("<> go n <> ")"
+      where go (NTypeSelector t) = toCssSelector t
+            go (NHash h) = toCssSelector h
+            go (NClass c) = toCssSelector c
+            go (NAttrib a) = toCssSelector a
+            go (NPseudo p) = toCssSelector p
+            go (NPseudoElement p) = toCssSelector p
+    toSelectorGroup = toSelectorGroup . SNot
+    specificity' (NTypeSelector t) = specificity' t
+    specificity' (NHash h) = specificity' h
+    specificity' (NClass c) = specificity' c
+    specificity' (NAttrib a) = specificity' a
+    specificity' (NPseudo p) = specificity' p
+    specificity' (NPseudoElement p) = specificity' p
+    toPattern (NTypeSelector t) = _conP 'NTypeSelector [toPattern t]
+    toPattern (NHash h) = _conP 'NHash [toPattern h]
+    toPattern (NClass c) = _conP 'NClass [toPattern c]
+    toPattern (NAttrib a) = _conP 'NAttrib [toPattern a]
+    toPattern (NPseudo p) = _conP 'NPseudo [toPattern p]
+    toPattern (NPseudoElement p) = _conP 'NPseudoElement [toPattern p]
+
+instance ToCssSelector PseudoElement where
+    toCssSelector = pack . (':' :) . (':' :) . go
+      where go After = "after"
+            go Before = "before"
+            go FirstLetter = "first-letter"
+            go FirstLine = "first-line"
+            go Marker = "marker"
+            go Placeholder = "placeholder"
+            go Selection = "selection"
+    specificity' = const (SelectorSpecificity 0 0 1)
+    toSelectorGroup = toSelectorGroup . (def :.::)
+    toPattern = _constantP . go
+      where go After = 'After
+            go Before = 'Before
+            go FirstLetter = 'FirstLetter
+            go FirstLine = 'FirstLine
+            go Marker = 'Marker
+            go Placeholder = 'Placeholder
+            go Selection = 'Selection
+
 -- Custom Eq and Ord instances
 instance Eq SelectorSpecificity where
     (==) = on (==) specificityValue
@@ -633,6 +1088,9 @@
 instance Default Selector where
     def = Selector def
 
+instance Default PseudoSelectorSequence where
+    def = Sequence def
+
 instance Default SelectorSequence where
     def = SimpleSelector def
 
@@ -654,6 +1112,10 @@
 instance Default AttributeCombinator where
     def = Exact
 
+-- | The default of the Nth instance is @n@, where all childs are selected.
+instance Default Nth where
+    def = Nth 1 0
+
 -- Binary instance
 _putEnum :: Enum a => a -> Put
 _putEnum = putWord8 . fromIntegral . fromEnum
@@ -661,6 +1123,10 @@
 _getEnum :: Enum a => Get a
 _getEnum = toEnum . fromIntegral <$> getWord8
 
+instance Binary Nth where
+  put (Nth n b) = put n >> put b
+  get = Nth <$> get <*> get
+
 instance Binary SelectorSpecificity where
   put (SelectorSpecificity a b c) = put a >> put b >> put c
   get = SelectorSpecificity <$> get <*> get <*> get
@@ -673,8 +1139,88 @@
     case w of
       0 -> Selector <$> get
       1 -> Combined <$> get <*> get <*> get
-      _ -> fail "An error occured while deserializing a Selector object"
+      _ -> fail "An error occured while deserializing a Selector object."
 
+instance Binary PseudoSelectorSequence where
+  put (Sequence ss) = putWord8 0 >> put ss
+  put (ss :.:: pe) = putWord8 1 >> put ss >> put pe
+  get = do
+    w <- getWord8
+    case w of
+      0 -> Sequence <$> get
+      1 -> (:.::) <$> get <*> get
+      _ -> fail "An error occured while deserializing a PseudoSelectorSequence."
+
+instance Binary PseudoClass where
+  put Active = putWord8 0
+  put Checked = putWord8 1
+  put Default = putWord8 2
+  put Disabled = putWord8 3
+  put Empty = putWord8 4
+  put Enabled = putWord8 5
+  put Focus = putWord8 6
+  put Fullscreen = putWord8 7
+  put Hover = putWord8 8
+  put Indeterminate = putWord8 9
+  put InRange = putWord8 10
+  put Invalid = putWord8 11
+  put (Lang l) = putWord8 12 >> put l
+  put Link = putWord8 13
+  put (NthChild nth) = putWord8 14 >> put nth
+  put (NthLastChild nth) = putWord8 15 >> put nth
+  put (NthLastOfType nth) = putWord8 16 >> put nth
+  put (NthOfType nth) = putWord8 17 >> put nth
+  put OnlyOfType = putWord8 18
+  put OnlyChild = putWord8 19
+  put Optional = putWord8 20
+  put OutOfRange = putWord8 21
+  put ReadOnly = putWord8 22
+  put ReadWrite = putWord8 23
+  put Required = putWord8 24
+  put Root = putWord8 25
+  put Target = putWord8 26
+  put Valid = putWord8 27
+  put Visited = putWord8 28
+
+  get = do
+    w <- getWord8
+    case w of
+      0 -> pure Active
+      1 -> pure Checked
+      2 -> pure Default
+      3 -> pure Disabled
+      4 -> pure Empty
+      5 -> pure Enabled
+      6 -> pure Focus
+      7 -> pure Fullscreen
+      8 -> pure Hover
+      9 -> pure Indeterminate
+      10 -> pure InRange
+      11 -> pure Invalid
+      12 -> Lang <$> get
+      13 -> pure Link
+      14 -> NthChild <$> get
+      15 -> NthLastChild <$> get
+      16 -> NthLastOfType <$> get
+      17 -> NthOfType <$> get
+      18 -> pure OnlyOfType
+      19 -> pure OnlyChild
+      20 -> pure Optional
+      21 -> pure OutOfRange
+      22 -> pure ReadOnly
+      23 -> pure ReadWrite
+      24 -> pure Required
+      25 -> pure Root
+      26 -> pure Target
+      27 -> pure Valid
+      28 -> pure Visited
+      _ -> fail "An error occured while deserialzing a PseudoClass object."
+
+
+instance Binary PseudoElement where
+  put = _putEnum
+  get = _getEnum
+
 instance Binary SelectorCombinator where
   put = _putEnum
   get = _getEnum
@@ -693,14 +1239,37 @@
   put (SHash h) = putWord8 0 >> put h
   put (SClass c) = putWord8 1 >> put c
   put (SAttrib a) = putWord8 2 >> put a
+  put (SPseudo p) = putWord8 3 >> put p
+  put (SNot n) = putWord8 4 >> put n
   get = do
     w <- getWord8
     case w of
       0 -> SHash <$> get
       1 -> SClass <$> get
       2 -> SAttrib <$> get
+      3 -> SPseudo <$> get
+      4 -> SNot <$> get
       _ -> fail "An error occurred when deserializing a SelectorFilter object."
 
+instance Binary Negation where
+  put (NTypeSelector t) = putWord8 0 >> put t
+  put (NHash h) = putWord8 1 >> put h
+  put (NClass c) = putWord8 2 >> put c
+  put (NAttrib a) = putWord8 3 >> put a
+  put (NPseudo p) = putWord8 4 >> put p
+  put (NPseudoElement p) = putWord8 5 >> put p
+  get = do
+    w <- getWord8
+    case w of
+      0 -> NTypeSelector <$> get
+      1 -> NHash <$> get
+      2 -> NClass <$> get
+      3 -> NAttrib <$> get
+      4 -> NPseudo <$> get
+      5 -> NPseudoElement <$> get
+      _ -> fail "An error occurred when deserializing a Negation object."
+
+
 instance Binary Attrib where
   put (Exist e) = putWord8 0 >> put e
   put (Attrib an ac av) = putWord8 1 >> put an >> put ac >> put av
@@ -755,9 +1324,12 @@
   put (SelectorGroup g) = put g
   get = SelectorGroup <$> get
 
-
 -- Lift instances
+#if MIN_VERSION_template_haskell(2,17,0)
+_apply :: Quote m => Name -> [m Exp] -> m Exp
+#else
 _apply :: Name -> [Q Exp] -> Q Exp
+#endif
 _apply = foldl appE . conE
 
 instance Lift SelectorGroup where
@@ -769,7 +1341,6 @@
     liftTyped = unsafeTExpCoerce . lift
 #endif
 
-
 instance Lift Selector where
 #if MIN_VERSION_template_haskell(2,17,0)
   liftTyped = unsafeCodeCoerce . lift
@@ -805,7 +1376,41 @@
   liftTyped = unsafeTExpCoerce . lift
 #endif
 
+instance Lift PseudoSelectorSequence where
+#if MIN_VERSION_template_haskell(2,17,0)
+  liftTyped = unsafeCodeCoerce . lift
+#elif MIN_VERSION_template_haskell(2,16,0)
+  liftTyped = unsafeTExpCoerce . lift
+#endif
 
+instance Lift PseudoClass where
+#if MIN_VERSION_template_haskell(2,17,0)
+  liftTyped = unsafeCodeCoerce . lift
+#elif MIN_VERSION_template_haskell(2,16,0)
+  liftTyped = unsafeTExpCoerce . lift
+#endif
+
+instance Lift PseudoElement where
+#if MIN_VERSION_template_haskell(2,17,0)
+  liftTyped = unsafeCodeCoerce . lift
+#elif MIN_VERSION_template_haskell(2,16,0)
+  liftTyped = unsafeTExpCoerce . lift
+#endif
+
+instance Lift Nth where
+#if MIN_VERSION_template_haskell(2,17,0)
+  liftTyped = unsafeCodeCoerce . lift
+#elif MIN_VERSION_template_haskell(2,16,0)
+  liftTyped = unsafeTExpCoerce . lift
+#endif
+
+instance Lift Negation where
+#if MIN_VERSION_template_haskell(2,17,0)
+  liftTyped = unsafeCodeCoerce . lift
+#elif MIN_VERSION_template_haskell(2,16,0)
+  liftTyped = unsafeTExpCoerce . lift
+#endif
+
 -- ToMarkup instances
 _cssToMarkup :: ToCssSelector a => a -> Markup
 _cssToMarkup = text . toCssSelector
@@ -819,12 +1424,24 @@
 instance ToMarkup SelectorSequence where
     toMarkup = _cssToMarkup
 
+instance ToMarkup PseudoSelectorSequence where
+    toMarkup = _cssToMarkup
+
+instance ToMarkup PseudoClass where
+    toMarkup = _cssToMarkup
+
+instance ToMarkup PseudoElement where
+    toMarkup = _cssToMarkup
+
 instance ToMarkup SelectorFilter where
     toMarkup = _cssToMarkup
 
 instance ToMarkup Attrib where
     toMarkup = _cssToMarkup
 
+instance ToMarkup Negation where
+    toMarkup = _cssToMarkup
+
 -- ToJavaScript and ToJson instances
 _cssToJavascript :: ToCssSelector a => a -> Javascript
 #if __GLASGOW_HASKELL__ < 803
@@ -845,12 +1462,24 @@
 instance ToJavascript SelectorSequence where
     toJavascript = _cssToJavascript
 
+instance ToJavascript PseudoSelectorSequence where
+    toJavascript = _cssToJavascript
+
+instance ToJavascript PseudoClass where
+    toJavascript = _cssToJavascript
+
+instance ToJavascript PseudoElement where
+    toJavascript = _cssToJavascript
+
 instance ToJavascript SelectorFilter where
     toJavascript = _cssToJavascript
 
 instance ToJavascript Attrib where
     toJavascript = _cssToJavascript
 
+instance ToJavascript Negation where
+    toJavascript = _cssToJavascript
+
 instance ToJSON SelectorGroup where
     toJSON = _cssToJson
 
@@ -863,14 +1492,29 @@
 instance ToJSON SelectorFilter where
     toJSON = _cssToJson
 
+instance ToJSON PseudoSelectorSequence where
+    toJSON = _cssToJson
+
+instance ToJSON PseudoClass where
+    toJSON = _cssToJson
+
+instance ToJSON PseudoElement where
+    toJSON = _cssToJson
+
 instance ToJSON Attrib where
     toJSON = _cssToJson
 
+instance ToJSON Negation where
+    toJSON = _cssToJson
 
+
 -- Arbitrary instances
 _arbitraryIdent :: Gen Text
 _arbitraryIdent = pack <$> listOf1 arbitrary
 
+_arbitraryLanguages :: [Text]
+_arbitraryLanguages = ["af", "af-ZA", "ar", "ar-AE", "ar-BH", "ar-DZ", "ar-EG", "ar-IQ", "ar-JO", "ar-KW", "ar-LB", "ar-LY", "ar-MA", "ar-OM", "ar-QA", "ar-SA", "ar-SY", "ar-TN", "ar-YE", "az", "az-AZ", "az-AZ", "be", "be-BY", "bg", "bg-BG", "bs-BA", "ca", "ca-ES", "cs", "cs-CZ", "cy", "cy-GB", "da", "da-DK", "de", "de-AT", "de-CH", "de-DE", "de-LI", "de-LU", "dv", "dv-MV", "el", "el-GR", "en", "en-AU", "en-BZ", "en-CA", "en-CB", "en-GB", "en-IE", "en-JM", "en-NZ", "en-PH", "en-TT", "en-US", "en-ZA", "en-ZW", "eo", "es", "es-AR", "es-BO", "es-CL", "es-CO", "es-CR", "es-DO", "es-EC", "es-ES", "es-ES", "es-GT", "es-HN", "es-MX", "es-NI", "es-PA", "es-PE", "es-PR", "es-PY", "es-SV", "es-UY", "es-VE", "et", "et-EE", "eu", "eu-ES", "fa", "fa-IR", "fi", "fi-FI", "fo", "fo-FO", "fr", "fr-BE", "fr-CA", "fr-CH", "fr-FR", "fr-LU", "fr-MC", "gl", "gl-ES", "gu", "gu-IN", "he", "he-IL", "hi", "hi-IN", "hr", "hr-BA", "hr-HR", "hu", "hu-HU", "hy", "hy-AM", "id", "id-ID", "is", "is-IS", "it", "it-CH", "it-IT", "ja", "ja-JP", "ka", "ka-GE", "kk", "kk-KZ", "kn", "kn-IN", "ko", "ko-KR", "kok", "kok-IN", "ky", "ky-KG", "lt", "lt-LT", "lv", "lv-LV", "mi", "mi-NZ", "mk", "mk-MK", "mn", "mn-MN", "mr", "mr-IN", "ms", "ms-BN", "ms-MY", "mt", "mt-MT", "nb", "nb-NO", "nl", "nl-BE", "nl-NL", "nn-NO", "ns", "ns-ZA", "pa", "pa-IN", "pl", "pl-PL", "ps", "ps-AR", "pt", "pt-BR", "pt-PT", "qu", "qu-BO", "qu-EC", "qu-PE", "ro", "ro-RO", "ru", "ru-RU", "sa", "sa-IN", "se", "se-FI", "se-FI", "se-FI", "se-NO", "se-NO", "se-NO", "se-SE", "se-SE", "se-SE", "sk", "sk-SK", "sl", "sl-SI", "sq", "sq-AL", "sr-BA", "sr-BA", "sr-SP", "sr-SP", "sv", "sv-FI", "sv-SE", "sw", "sw-KE", "syr", "syr-SY", "ta", "ta-IN", "te", "te-IN", "th", "th-TH", "tl", "tl-PH", "tn", "tn-ZA", "tr", "tr-TR", "tt", "tt-RU", "ts", "uk", "uk-UA", "ur", "ur-PK", "uz", "uz-UZ", "uz-UZ", "vi", "vi-VN", "xh", "xh-ZA", "zh", "zh-CN", "zh-HK", "zh-MO", "zh-SG", "zh-TW", "zu", "zu-ZA"]
+
 _shrinkText :: Text -> [Text]
 _shrinkText = liftA2 (zipWith (<>)) inits (tails . T.drop 1)
 
@@ -887,6 +1531,13 @@
     arbitrary = Class <$> _arbitraryIdent
     shrink (Class a) = Class <$> _shrinkIdent a
 
+instance Arbitrary Nth where
+    arbitrary = Nth <$> ((1+) . abs <$> arbitrary) <*> arbitrary
+    shrink nth
+      | nth == nnth = []
+      | otherwise = [nnth]
+      where nnth = normalizeNth nth
+
 instance Arbitrary Namespace where
     arbitrary = frequency [(3, pure NAny), (1, Namespace <$> _arbitraryIdent)]
     shrink NAny = []
@@ -903,9 +1554,14 @@
 
 instance Arbitrary SelectorSequence where
     arbitrary = addFilters . SimpleSelector <$> arbitrary <*> listOf arbitrary
-    shrink (SimpleSelector _) = []
-    shrink (Filter ss sf) = ss : (Filter ss <$> shrink sf)
+    shrink (SimpleSelector ss) = SimpleSelector <$> shrink ss
+    shrink (Filter ss sf) = ss : ((`Filter` sf) <$> shrink ss) ++ (Filter ss <$> shrink sf)
 
+instance Arbitrary PseudoSelectorSequence where
+    arbitrary = frequency [(3, Sequence <$> arbitrary), (1, (:.::) <$> arbitrary <*> arbitrary)]
+    shrink (Sequence ss) = Sequence <$> shrink ss
+    shrink (ss :.:: pe) = Sequence ss : ((ss :.::) <$> shrink pe) ++ ((:.:: pe) <$> shrink ss)
+
 instance Arbitrary SelectorCombinator where
     arbitrary = arbitraryBoundedEnum
 
@@ -913,11 +1569,22 @@
     arbitrary = arbitraryBoundedEnum
 
 instance Arbitrary SelectorFilter where
-    arbitrary = oneof [SHash <$> arbitrary, SClass <$> arbitrary, SAttrib <$> arbitrary]
+    arbitrary = frequency [(4, SHash <$> arbitrary), (4, SClass <$> arbitrary), (4, SAttrib <$> arbitrary), (4, SPseudo <$> arbitrary), (1, SNot <$> arbitrary)]
     shrink (SHash x) = SHash <$> shrink x
     shrink (SClass x) = SClass <$> shrink x
     shrink (SAttrib x) = SAttrib <$> shrink x
+    shrink (SPseudo x) = SPseudo <$> shrink x
+    shrink (SNot x) = SNot <$> shrink x
 
+instance Arbitrary Negation where
+    arbitrary = oneof [NTypeSelector <$> arbitrary, NHash <$> arbitrary, NClass <$> arbitrary, NAttrib <$> arbitrary, NPseudo <$> arbitrary, NPseudoElement <$> arbitrary]
+    shrink (NTypeSelector x) = NTypeSelector <$> shrink x
+    shrink (NHash x) = NHash <$> shrink x
+    shrink (NClass x) = NClass <$> shrink x
+    shrink (NAttrib x) = NAttrib <$> shrink x
+    shrink (NPseudo x) = NPseudo <$> shrink x
+    shrink (NPseudoElement x) = NPseudoElement <$> shrink x
+
 instance Arbitrary AttributeName where
     arbitrary = AttributeName <$> arbitrary <*> _arbitraryIdent
     shrink (AttributeName x y) = (AttributeName x <$> _shrinkIdent y) ++ ((`AttributeName` y) <$> shrink x)
@@ -937,3 +1604,12 @@
     arbitrary = frequency [(3, Selector <$> arbitrary), (1, Combined <$> arbitrary <*> arbitrary <*> arbitrary) ]
     shrink (Selector x) = Selector <$> shrink x
     shrink (Combined x y z) = z : (Combined x y <$> shrink z) ++ ((\sx -> Combined sx y z) <$> shrink x)
+
+instance Arbitrary PseudoClass where
+    arbitrary = oneof ((Lang <$> elements _arbitraryLanguages) : map pure [
+        Active, Checked, Default, Disabled, Empty, Enabled, Focus, Fullscreen, Hover, Indeterminate, InRange, Invalid, Link, OnlyOfType, OnlyChild
+      , Optional, OutOfRange, ReadOnly, ReadWrite, Required, Root, Target, Valid, Visited
+      ] ++ map (<$> arbitrary) [NthChild, NthLastChild, NthLastOfType, NthOfType])
+
+instance Arbitrary PseudoElement where
+    arbitrary = arbitraryBoundedEnum
diff --git a/src/Css3/Selector/Lexer.x b/src/Css3/Selector/Lexer.x
--- a/src/Css3/Selector/Lexer.x
+++ b/src/Css3/Selector/Lexer.x
@@ -1,23 +1,49 @@
 --vim:ft=haskell
 {
-module Css3.Selector.Lexer(AlexPosn(..), Token(..), TokenLoc(..), alexScanTokens) where
+{-# OPTIONS_GHC -fno-warn-unused-imports #-}
+{-# LANGUAGE PatternSynonyms #-}
 
-import Data.Decimal(Decimal)
+module Css3.Selector.Lexer(
+    AlexPosn(AlexPn)
+  , Token(
+      TIncludes, TEqual, TDashMatch, TPrefixMatch, TSuffixMatch, TSubstringMatch, Ident, String, THash, Decimal
+    , Integer, Comma, Plus, Greater, Tilde, Dot, Pipe, Asterisk, Space, BOpen, BClose, PseudoClass, PseudoFunction
+    , PseudoElement, TN, TNth, TPM, TInt, TClose, TNot, TLang
+    )
+  , TokenLoc(TokenLoc)
+  , alexScanTokens
+  ) where
+
 import Css3.Selector.Utils(readCssString, readIdentifier)
+import Css3.Selector.Core(
+    PseudoElement(After, Before, FirstLetter, FirstLine, Marker, Placeholder, Selection)
+  , PseudoClass(
+        Active, Checked, Default, Disabled, Empty, Enabled, Focus, Fullscreen, Hover, Indeterminate, InRange
+      , Invalid, Link, NthChild, NthLastChild, NthLastOfType, NthOfType, OnlyOfType, OnlyChild, Optional
+      , OutOfRange, ReadOnly, ReadWrite, Required, Root, Target, Valid, Visited
+      )
+  , Nth, pattern Even, pattern Odd
+  , pattern FirstChild, pattern FirstOfType, pattern LastChild, pattern LastOfType
+  )
+
+import Data.Decimal(Decimal)
+#if __GLASGOW_HASKELL__ < 803
+import Data.Semigroup(Semigroup((<>)))
+#endif
 }
 
-%wrapper "posn"
+%wrapper "monadUserState"
 
 $nonascii = [^\0-\xff]
 $w        = [\ \t\r\n\f]
 $nostar   = [^\*]
 $nostars  = [^\/\*]
 $tl       = [\~]
+$pm       = [\-\+]
 
 @nl       = \r|\n|\r\n|\f
 @unicode  = \\[0-9a-fA-F]{1,6}(\r\n|[ \n\r\t\f])?
 @escape   = @unicode | \\[^\n\r\f0-9a-fA-F]
-
 @wo = $w*
 @nonaesc = $nonascii | @escape
 @nmstart = [_a-zA-Z] | @nonaesc
@@ -30,52 +56,139 @@
 @string2 = \"([^\n\r\f\\\"] | \\@nl | @nonaesc )*\"   -- strings with double quotes
 @string  = @string1 | @string2
 
+
+@a       = a|A|\\0{0,4}(41|61)(\r\n|[ \t\r\n\f])?
+@b       = b|B|\\0{0,4}(42|62)(\r\n|[ \t\r\n\f])?
+@c       = c|C|\\0{0,4}(43|63)(\r\n|[ \t\r\n\f])?
 @d       = d|D|\\0{0,4}(44|64)(\r\n|[ \t\r\n\f])?
 @e       = e|E|\\0{0,4}(45|65)(\r\n|[ \t\r\n\f])?
+@f       = f|F|\\0{0,4}(46|66)(\r\n|[ \t\r\n\f])?
+@g       = g|G|\\0{0,4}(47|67)(\r\n|[ \t\r\n\f])?
+@h       = h|H|\\0{0,4}(48|68)(\r\n|[ \t\r\n\f])?
+@i       = i|I|\\0{0,4}(49|69)(\r\n|[ \t\r\n\f])?
+@j       = j|J|\\0{0,4}(4a|6a)(\r\n|[ \t\r\n\f])?
+@k       = k|K|\\0{0,4}(4b|6b)(\r\n|[ \t\r\n\f])?
+@l       = l|L|\\0{0,4}(4c|6c)(\r\n|[ \t\r\n\f])?
+@m       = m|M|\\0{0,4}(4d|6d)(\r\n|[ \t\r\n\f])?
 @n       = n|N|\\0{0,4}(4e|6e)(\r\n|[ \t\r\n\f])?|\\n
 @o       = o|O|\\0{0,4}(4f|6f)(\r\n|[ \t\r\n\f])?|\\o
+@p       = p|P|\\0{0,4}(50|70)(\r\n|[ \t\r\n\f])?
+@q       = q|Q|\\0{0,4}(51|71)(\r\n|[ \t\r\n\f])?
+@r       = r|R|\\0{0,4}(52|72)(\r\n|[ \t\r\n\f])?
+@s       = s|S|\\0{0,4}(53|73)(\r\n|[ \t\r\n\f])?
 @t       = t|T|\\0{0,4}(54|74)(\r\n|[ \t\r\n\f])?|\\t
-@v       = v|V|\\0{0,4}(58|78)(\r\n|[ \t\r\n\f])?|\\v
+@u       = u|U|\\0{0,4}(55|75)(\r\n|[ \t\r\n\f])?
+@v       = v|V|\\0{0,4}(56|76)(\r\n|[ \t\r\n\f])?|\\v
+@w       = w|W|\\0{0,4}(57|77)(\r\n|[ \t\r\n\f])?
+@x       = x|X|\\0{0,4}(58|78)(\r\n|[ \t\r\n\f])?
+@y       = y|Y|\\0{0,4}(59|79)(\r\n|[ \t\r\n\f])?
+@z       = z|Z|\\0{0,4}(5a|7a)(\r\n|[ \t\r\n\f])?
+@hyphen  = [\-]|\\0{0,4}2d
+
+@firsth  = @f@i@r@s@t@hyphen
+@nthh    = @n@t@h@hyphen
+@onlyh   = @o@n@l@y@hyphen
+@child   = @c@h@i@l@d
+@oftype  = @o@f@hyphen@t@y@p@e
+@lasth   = @l@a@s@t@hyphen
+
 @cmo     = \/\*
 @cmc     = \*\/
-
+@psc     = [:]
+@pse     = [:][:]
+@psb     = [:][:]?
+@lang    = [A-Za-z\-]+
 
 tokens :-
-  @wo "="  @wo     { constoken TEqual }
-  @wo "~=" @wo     { constoken TIncludes }
-  @wo "|=" @wo     { constoken TDashMatch }
-  @wo "^=" @wo     { constoken TPrefixMatch }
-  @wo "$=" @wo     { constoken TSuffixMatch }
-  @wo "*=" @wo     { constoken TSubstringMatch }
-  @wo ","  @wo     { constoken Comma }
-  "."              { constoken Dot }
-  "|"              { constoken Pipe }
-  "*"              { constoken Asterisk }
-  @ident           { tokenize (Ident . readIdentifier) }
-  @string          { tokenize (String . readCssString) }
-  "#" @name        { tokenize (THash . readIdentifier . drop 1) }
-  @float           { tokenize (Decimal . read) }
-  @int             { tokenize (Integer . read) }
-  @wo "+" @wo      { constoken Plus }
-  @wo ">" @wo      { constoken Greater }
-  @wo $tl @wo      { constoken Tilde }
-  "[" @wo          { constoken BOpen }
-  @wo "]"          { constoken BClose }
-  $w @wo           { constoken Space }
-  @cmo $nostar* \*+ ($nostars $nostar* \*+)* @cmc      ;
-
+ <0> {
+  @wo "="  @wo                            { constoken TEqual }
+  @wo "~=" @wo                            { constoken TIncludes }
+  @wo "|=" @wo                            { constoken TDashMatch }
+  @wo "^=" @wo                            { constoken TPrefixMatch }
+  @wo "$=" @wo                            { constoken TSuffixMatch }
+  @wo "*=" @wo                            { constoken TSubstringMatch }
+  @wo ","  @wo                            { constoken Comma }
+  "."                                     { constoken Dot }
+  "|"                                     { constoken Pipe }
+  "*"                                     { constoken Asterisk }
+  @ident                                  { tokenize (Ident . readIdentifier) }
+  @string                                 { tokenize (String . readCssString) }
+  "#" @name                               { tokenize (THash . readIdentifier . drop 1) }
+  @float                                  { tokenize (Decimal . read) }
+  @int                                    { tokenize (Integer . read) }
+  @wo "+" @wo                             { constoken Plus }
+  @wo ">" @wo                             { constoken Greater }
+  @wo $tl @wo                             { constoken Tilde }
+  "[" @wo                                 { constoken BOpen }
+  @wo "]"                                 { constoken BClose }
+  @psb @a@f@t@e@r                         { constoken (PseudoElement After) }
+  @psb @b@e@f@o@r@e                       { constoken (PseudoElement Before) }
+  @psb @firsth@l@e@t@t@e@r                { constoken (PseudoElement FirstLetter) }
+  @psb @firsth@l@i@n@e                    { constoken (PseudoElement FirstLine) }
+  @pse @m@a@r@k@e@r                       { constoken (PseudoElement Marker) }
+  @pse @p@l@a@c@e@h@o@l@d@e@r             { constoken (PseudoElement Placeholder) }
+  @pse @s@e@l@e@c@t@i@o@n                 { constoken (PseudoElement Selection) }
+  @psc @a@c@t@i@v@e                       { constoken (PseudoClass Active) }
+  @psc @c@h@e@c@k@e@d                     { constoken (PseudoClass Checked) }
+  @psc @d@e@f@a@u@l@t                     { constoken (PseudoClass Default) }
+  @psc @d@i@s@a@b@l@e@d                   { constoken (PseudoClass Disabled) }
+  @psc @e@m@p@t@y                         { constoken (PseudoClass Empty) }
+  @psc @e@n@a@b@l@e@d                     { constoken (PseudoClass Enabled) }
+  @psc @firsth@child                      { constoken (PseudoClass FirstChild) }
+  @psc @firsth@oftype                     { constoken (PseudoClass FirstOfType) }
+  @psc @f@o@c@u@s                         { constoken (PseudoClass Focus) }
+  @psc @f@u@l@l@s@c@r@e@e@n               { constoken (PseudoClass Fullscreen) }
+  @psc @h@o@v@e@r                         { constoken (PseudoClass Hover) }
+  @psc @i@n@d@e@t@e@r@m@i@n@a@t@e         { constoken (PseudoClass Indeterminate) }
+  @psc @i@n@hyphen@r@a@n@g@e              { constoken (PseudoClass InRange) }
+  @psc @i@n@v@a@l@i@d                     { constoken (PseudoClass Invalid) }
+  @psc @lasth@child                       { constoken (PseudoClass LastChild) }
+  @psc @lasth@oftype                      { constoken (PseudoClass LastOfType) }
+  @psc @l@i@n@k                           { constoken (PseudoClass Link) }
+  @psc @l@a@n@g "("                       { constAndBegin TLang lang_state }
+  @psc @nthh@child "("                    { constAndBegin (PseudoFunction NthChild) nth_state }
+  @psc @nthh@lasth@child "("              { constAndBegin (PseudoFunction NthLastChild) nth_state }
+  @psc @nthh@lasth@oftype "("             { constAndBegin (PseudoFunction NthLastOfType) nth_state }
+  @psc @nthh@oftype "("                   { constAndBegin (PseudoFunction NthOfType) nth_state }
+  @psc @n@o@t "(" @wo                     { constoken TNot }
+  @wo ")"                                 { constoken TClose }
+  @psc @onlyh@oftype                      { constoken (PseudoClass OnlyOfType) }
+  @psc @onlyh@child                       { constoken (PseudoClass OnlyChild) }
+  @psc @o@p@t@i@o@n@a@l                   { constoken (PseudoClass Optional) }
+  @psc @o@u@t@hyphen@o@f@hyphen@r@a@n@g@e { constoken (PseudoClass OutOfRange) }
+  @psc @r@e@a@d@hyphen@o@n@l@y            { constoken (PseudoClass ReadOnly) }
+  @psc @r@e@a@d@hyphen@w@r@i@t@e          { constoken (PseudoClass ReadWrite) }
+  @psc @r@e@q@u@i@r@e@d                   { constoken (PseudoClass Required) }
+  @psc @r@o@o@t                           { constoken (PseudoClass Root) }
+  @psc @t@a@r@g@e@t                       { constoken (PseudoClass Target) }
+  @psc @v@a@l@i@d                         { constoken (PseudoClass Valid) }
+  @psc @v@i@s@i@t@e@d                     { constoken (PseudoClass Visited) }
+  $w @wo                                  { constoken Space }
+  @cmo $nostar* \*+ ($nostars $nostar* \*+)* @cmc;
+ }
+ <nth_state> {
+  $w @wo                                  { constoken Space }
+  @e@v@e@n                                { constoken (TNth Even) }
+  @o@d@d                                  { constoken (TNth Odd) }
+  @n                                      { constoken TN }
+  "+"                                     { constoken (TPM id) }
+  "-"                                     { constoken (TPM negate) }
+  @int                                    { tokenize (TInt . read) }
+  ")"                                     { constAndBegin TClose state_initial }
+ }
+ <lang_state> {
+  @lang                                   { tokenize String }
+  $w @wo                                  { skip }
+  ")"                                     { constAndBegin TClose state_initial }
+ }
 {
-data TokenLoc = TokenLoc { token :: Token, original :: String, location :: AlexPosn }
 
-tokenize :: (String -> Token) -> AlexPosn -> String -> TokenLoc
-tokenize = flip . (>>= TokenLoc)
+data TokenLoc = TokenLoc Token String (Maybe AlexPosn)
 
-constoken :: Token -> AlexPosn -> String -> TokenLoc
-constoken = tokenize . const
+type AlexUserState = ()
 
--- The token type:
-data Token =
-      TIncludes
+data Token
+    = TIncludes
     | TEqual
     | TDashMatch
     | TPrefixMatch
@@ -96,5 +209,40 @@
     | Space
     | BOpen
     | BClose
-    deriving (Eq,Show)
+    | PseudoClass PseudoClass
+    | PseudoFunction (Nth -> PseudoClass)
+    | PseudoElement PseudoElement
+    | TN
+    | TNth Nth
+    | TPM (Int -> Int)
+    | TInt Int
+    | TClose
+    | TNot
+    | TLang
+
+tokenize :: (String -> Token) -> AlexInput -> Int -> Alex TokenLoc
+tokenize f (p, _, _, str) len = pure (TokenLoc (f str') str' (Just p))
+  where str' = take len str
+
+constoken :: Token -> AlexInput -> Int -> Alex TokenLoc
+constoken = tokenize . const
+
+constAndBegin :: Token -> Int -> AlexInput -> Int -> Alex TokenLoc
+constAndBegin = andBegin . constoken
+
+state_initial :: Int
+state_initial = 0
+
+alexInitUserState :: AlexUserState
+alexInitUserState = ()
+
+alexEOF :: Alex TokenLoc
+alexEOF = pure (TokenLoc undefined "" Nothing)
+
+alexScanTokens :: String -> Either String [TokenLoc]
+alexScanTokens str = runAlex str loop
+  where loop :: Alex [TokenLoc]
+        loop = alexMonadScan >>= p
+        p (TokenLoc _ _ Nothing) = pure []
+        p toc = (toc:) <$> loop
 }
diff --git a/src/Css3/Selector/Parser.y b/src/Css3/Selector/Parser.y
--- a/src/Css3/Selector/Parser.y
+++ b/src/Css3/Selector/Parser.y
@@ -3,10 +3,18 @@
 module Css3.Selector.Parser where
 
 import Css3.Selector.Core
-import Css3.Selector.Lexer(AlexPosn(..), Token(..), TokenLoc(..))
+import Css3.Selector.Lexer(
+    AlexPosn(AlexPn), TokenLoc(TokenLoc)
+  , Token(
+      TIncludes, TEqual, TDashMatch, TPrefixMatch, TSuffixMatch, TSubstringMatch, Ident, String, THash, Decimal
+    , Integer, Comma, Plus, Greater, Tilde, Dot, Pipe, Asterisk, Space, BOpen, BClose, PseudoClass, PseudoFunction
+    , PseudoElement, TN, TNth, TPM, TInt, TClose, TNot, TLang
+    )
+  )
 
 import Data.List.NonEmpty(NonEmpty((:|)), (<|))
 
+import Data.Default.Class(def)
 #if __GLASGOW_HASKELL__ < 803
 import Data.Semigroup((<>))
 #endif
@@ -18,25 +26,35 @@
 %error { happyError }
 
 %token
-    ','    { TokenLoc Comma _ _ }
-    '>'    { TokenLoc Greater _ _ }
-    '+'    { TokenLoc Plus _ _ }
-    '~'    { TokenLoc Tilde _ _ }
-    '.'    { TokenLoc Dot _ _ }
-    ' '    { TokenLoc Space _ _ }
-    '|'    { TokenLoc Pipe _ _ }
-    '*'    { TokenLoc Asterisk _ _ }
-    '['    { TokenLoc BOpen _ _ }
-    ']'    { TokenLoc BClose _ _ }
-    '='    { TokenLoc TEqual _ _ }
-    '^='   { TokenLoc TPrefixMatch _ _ }
-    '$='   { TokenLoc TSuffixMatch _ _ }
-    '*='   { TokenLoc TSubstringMatch _ _ }
-    '|='   { TokenLoc TDashMatch _ _ }
-    '~='   { TokenLoc TIncludes _ _ }
-    ident  { TokenLoc (Ident $$) _ _ }
-    string { TokenLoc (String $$) _ _ }
-    hash   { TokenLoc (THash $$) _ _ }
+    ','     { TokenLoc Comma _ _ }
+    '>'     { TokenLoc Greater _ _ }
+    '+'     { TokenLoc Plus _ _ }
+    '~'     { TokenLoc Tilde _ _ }
+    '.'     { TokenLoc Dot _ _ }
+    ' '     { TokenLoc Space _ _ }
+    '|'     { TokenLoc Pipe _ _ }
+    '*'     { TokenLoc Asterisk _ _ }
+    '['     { TokenLoc BOpen _ _ }
+    ']'     { TokenLoc BClose _ _ }
+    '='     { TokenLoc TEqual _ _ }
+    '^='    { TokenLoc TPrefixMatch _ _ }
+    '$='    { TokenLoc TSuffixMatch _ _ }
+    '*='    { TokenLoc TSubstringMatch _ _ }
+    '|='    { TokenLoc TDashMatch _ _ }
+    '~='    { TokenLoc TIncludes _ _ }
+    ident   { TokenLoc (Ident $$) _ _ }
+    string  { TokenLoc (String $$) _ _ }
+    hash    { TokenLoc (THash $$) _ _ }
+    pseude  { TokenLoc (PseudoElement $$) _ _ }
+    pseudc  { TokenLoc (PseudoClass $$) _ _ }
+    pseudf  { TokenLoc (PseudoFunction $$) _ _ }
+    pm      { TokenLoc (TPM $$) _ _ }
+    'n'     { TokenLoc TN _ _ }
+    int     { TokenLoc (TInt $$) _ _ }
+    nth     { TokenLoc (TNth $$) _ _ }
+    'not('  { TokenLoc TNot _ _ }
+    'lang(' { TokenLoc TLang _ _ }
+    ')'     { TokenLoc TClose _ _ }
 
 %%
 
@@ -50,8 +68,8 @@
     ;
 
 Selector
-    : SimpleSelectorSequence                      { Selector $1 }
-    | SimpleSelectorSequence Combinator Selector  { Combined $1 $2 $3 }
+    : PseudoSelectorSequence                      { Selector $1 }
+    | PseudoSelectorSequence Combinator Selector  { Combined $1 $2 $3 }
     ;
 
 Combinator
@@ -61,6 +79,12 @@
     | ' '          { Descendant }
     ;
 
+PseudoSelectorSequence
+    : SimpleSelectorSequence        { Sequence $1 }
+    | SimpleSelectorSequence pseude { $1 :.:: $2 }
+    | pseude                        { def :.:: $1 }
+    ;
+
 SimpleSelectorSequence
     : Type FilterList             { addFilters (SimpleSelector $1) $2 }
     | SelectorAddition FilterList { addFilters (SimpleSelector Universal) ($1:$2) }
@@ -73,12 +97,49 @@
 
 SelectorAddition
     : hash                        { SHash (Hash (pack $1)) }
+    | pseudc                      { SPseudo $1 }
+    | pseudf OptSpace Nth         { SPseudo ($1 $3) }
     | Class                       { SClass $1 }
     | AttribBox                   { SAttrib $1 }
+    | 'not(' Negation ')'         { SNot $2 }
+    | 'lang(' string ')'          { SPseudo (Lang (pack $2)) }
     ;
 
+Negation
+    : hash                        { NHash (Hash (pack $1)) }
+    | Class                       { NClass $1 }
+    | AttribBox                   { NAttrib $1 }
+    | pseudc                      { NPseudo $1 }
+    | pseudf OptSpace Nth         { NPseudo ($1 $3) }
+    | Type                        { NTypeSelector $1 }
+    | pseude                      { NPseudoElement $1 }
+    | 'lang(' string ')'          { NPseudo (Lang (pack $2)) }
+    ;
+
+Nth
+    : nth OptSpace ')'                                       { $1 }
+    | PMOpt IntOpt 'n' OptSpace ')'                          { Nth ($1 $2) 0 }
+    | PMOpt IntOpt 'n' OptSpace pm OptSpace int OptSpace ')' { Nth ($1 $2) ($5 $7) }
+    | PMOpt int OptSpace ')'                                 { Nth 0 ($1 $2) }
+    ;
+
+PMOpt
+    :                             { id }
+    | pm                          { $1 }
+    ;
+
+IntOpt
+    :                             { 1 }
+    | int                         { $1 }
+    ;
+
+OptSpace
+    :                             { () }
+    | ' '                         { () }
+    ;
+
 AttribBox
-    : '[' Attrib ']'                       { $2 }
+    : '[' Attrib ']'              { $2 }
     ;
 
 Attrib
@@ -127,9 +188,7 @@
     ;
 
 {
-
 happyError :: [TokenLoc] -> a
-happyError [] = error "Unexpected end of string when parsing a css selector."
-happyError (~(TokenLoc _ s ~(AlexPn _ l c)):_) = error ("Can not parse the CSS selector: unpexected token \"" <> s <> "\" at location (" <> show l <> ", " <> show c <> ")")
-
+happyError (~(TokenLoc t s ~(Just (AlexPn _ l c))):_) = error ("Can not parse the CSS selector: unpexected token \"" <> s <> "\" at location (" <> show l <> ", " <> show c <> ")")
+happyError _ = error "Unexpected end of string when parsing a css selector."
 }
diff --git a/src/Css3/Selector/QuasiQuoters.hs b/src/Css3/Selector/QuasiQuoters.hs
--- a/src/Css3/Selector/QuasiQuoters.hs
+++ b/src/Css3/Selector/QuasiQuoters.hs
@@ -26,7 +26,10 @@
 -- | Parse the string to a 'SelectorGroup'.
 parseCss :: String -- ^ The string to be parsed to a 'SelectorGroup'
     -> SelectorGroup -- ^ The selectorgroup that is the equivalent of the given 'String'.
-parseCss = cssselector . alexScanTokens . filter ('\r' /=)
+parseCss st = al (alexScanTokens st')
+  where st' = filter ('\r' /=) st
+        al (Left er) = error er
+        al (Right val) = cssselector val
 
 liftDataWithText :: Data a => a -> Q Exp
 liftDataWithText = dataToExpQ ((((AppE (VarE 'pack) <$>) . lift . unpack) <$>) . cast)
diff --git a/src/Css3/Selector/Utils.hs b/src/Css3/Selector/Utils.hs
--- a/src/Css3/Selector/Utils.hs
+++ b/src/Css3/Selector/Utils.hs
@@ -119,4 +119,4 @@
     -> String -- ^ The string to validate, and wrap into the given function.
     -> a -- ^ The identifier object to return if the identifier is valid.
 toIdentifier f ident | isValidIdentifier ident = f (pack ident)
-                     | otherwise = error ("The identifier " <> show ident <> " is not a valid identifier.")
+                     | otherwise = error ("The identifier \"" <> show ident <> "\" is not a valid identifier.")
diff --git a/test/Spec.hs b/test/Spec.hs
--- a/test/Spec.hs
+++ b/test/Spec.hs
@@ -8,7 +8,12 @@
 import Data.Hashable(Hashable(hashWithSalt))
 import Data.Text(pack, unpack)
 
+import Debug.Trace(trace)
+
 import Test.Framework (defaultMain, testGroup)
+import Test.Framework.Options
+import Test.Framework.Runners.Options
+
 import Test.Framework.Providers.QuickCheck2 (testProperty)
 import Test.QuickCheck
 
@@ -22,71 +27,356 @@
         testProperty "Encode-decode identifier" encodeDecodeId
     ],
     testGroup "Arbitrary css parsing" [
-        testProperty "Encode-decode css identity" encodeDecodeCss,
-        testProperty "Encode-decode css identity: selector group" (encodeDecodeCss' @SelectorGroup),
-        testProperty "Encode-decode css identity: selector" (encodeDecodeCss' @Selector),
-        testProperty "Encode-decode css identity: selector sequence" (encodeDecodeCss' @SelectorSequence),
-        testProperty "Encode-decode css identity: selector filter" (encodeDecodeCss' @SelectorFilter),
-        testProperty "Encode-decode css identity: namespace" (encodeDecodeCss' @Namespace),
-        testProperty "Encode-decode css identity: element name" (encodeDecodeCss' @ElementName),
-        testProperty "Encode-decode css identity: type selector" (encodeDecodeCss' @TypeSelector),
-        testProperty "Encode-decode css identity: attribute" (encodeDecodeCss' @Attrib),
-        testProperty "Encode-decode css identity: attribute name" (encodeDecodeCss' @AttributeName),
-        testProperty "Encode-decode css identity: class" (encodeDecodeCss' @Class),
-        testProperty "Encode-decode css identity: hash" (encodeDecodeCss' @Hash)
+        testProperty "Encode-decode css identity" encodeDecodeCss
+      , testProperty "Encode-decode css identity: selector group" (encodeDecodeCss' @SelectorGroup)
+      , testProperty "Encode-decode css identity: selector" (encodeDecodeCss' @Selector)
+      , testProperty "Encode-decode css identity: selector sequence" (encodeDecodeCss' @SelectorSequence)
+      , testProperty "Encode-decode css identity: selector filter" (encodeDecodeCss' @SelectorFilter)
+      , testProperty "Encode-decode css identity: namespace" (encodeDecodeCss' @Namespace)
+      , testProperty "Encode-decode css identity: element name" (encodeDecodeCss' @ElementName)
+      , testProperty "Encode-decode css identity: type selector" (encodeDecodeCss' @TypeSelector)
+      , testProperty "Encode-decode css identity: attribute" (encodeDecodeCss' @Attrib)
+      , testProperty "Encode-decode css identity: attribute name" (encodeDecodeCss' @AttributeName)
+      , testProperty "Encode-decode css identity: class" (encodeDecodeCss' @Class)
+      , testProperty "Encode-decode css identity: pseudo class" (encodeDecodeCss' @PseudoClass)
+      , testProperty "Encode-decode css identity: pseudo element" (encodeDecodeCss' @PseudoElement)
+      , testProperty "Encode-decode css identity: pseudo selector sequence" (encodeDecodeCss' @PseudoSelectorSequence)
+      , testProperty "Encode-decode css identity: negation" (encodeDecodeCss' @Negation)
     ],
     testGroup "SelectorSequences" [
         testProperty "Adding and removing filters" addRemFilters
     ],
     testGroup "Normalization" [
-        testProperty "Normalized variant has the same specificity" normSpec,
-        testProperty "Normalization is idempotent" normIdem
+        testProperty "Normalized variant has the same specificity" normSpec
+      , testProperty "Normalization is idempotent" normIdem
     ],
     testGroup "Build an expression or pattern" [
-        testProperty "Check build of pattern 1" buildPattern1,
-        testProperty "Check build of pattern 2" buildPattern2
+        testProperty "Check build of pattern 1" buildPattern1
+      , testProperty "Check build of pattern 2" buildPattern2
     ],
     testGroup "Convert to binary and back" [
-        testProperty "Binary identity: selector group" (binaryEquivalent @SelectorGroup),
-        testProperty "Binary identity: selector" (binaryEquivalent @Selector),
-        testProperty "Binary identity: selector sequence" (binaryEquivalent @SelectorSequence),
-        testProperty "Binary identity: selector filter" (binaryEquivalent @SelectorFilter),
-        testProperty "Binary identity: namespace" (binaryEquivalent @Namespace),
-        testProperty "Binary identity: element name" (binaryEquivalent @ElementName),
-        testProperty "Binary identity: type selector" (binaryEquivalent @TypeSelector),
-        testProperty "Binary identity: attribute" (binaryEquivalent @Attrib),
-        testProperty "Binary identity: attribute name" (binaryEquivalent @AttributeName),
-        testProperty "Binary identity: class" (binaryEquivalent @Class),
-        testProperty "Binary identity: hash" (binaryEquivalent @Hash)
+        testProperty "Binary identity: selector group" (binaryEquivalent @SelectorGroup)
+      , testProperty "Binary identity: selector" (binaryEquivalent @Selector)
+      , testProperty "Binary identity: selector sequence" (binaryEquivalent @SelectorSequence)
+      , testProperty "Binary identity: selector filter" (binaryEquivalent @SelectorFilter)
+      , testProperty "Binary identity: namespace" (binaryEquivalent @Namespace)
+      , testProperty "Binary identity: element name" (binaryEquivalent @ElementName)
+      , testProperty "Binary identity: type selector" (binaryEquivalent @TypeSelector)
+      , testProperty "Binary identity: attribute" (binaryEquivalent @Attrib)
+      , testProperty "Binary identity: attribute name" (binaryEquivalent @AttributeName)
+      , testProperty "Binary identity: class" (binaryEquivalent @Class)
+      , testProperty "Binary identity: hash" (binaryEquivalent @Hash)
+      , testProperty "Binary identity: pseudo class" (binaryEquivalent @PseudoClass)
+      , testProperty "Binary identity: pseudo element" (binaryEquivalent @PseudoElement)
+      , testProperty "Binary identity: pseudo selector sequence" (binaryEquivalent @PseudoSelectorSequence)
+      , testProperty "Binary identity: nth" (binaryEquivalent @Nth)
+      , testProperty "Binary identity: negation" (binaryEquivalent @Negation)
     ],
     testGroup "Check binary equality" [
-        testProperty "Binary uniqness: selector group" (uniqnessEncoding @SelectorGroup),
-        testProperty "Binary uniqness: selector" (uniqnessEncoding @Selector),
-        testProperty "Binary uniqness: selector sequence" (uniqnessEncoding @SelectorSequence),
-        testProperty "Binary uniqness: selector filter" (uniqnessEncoding @SelectorFilter),
-        testProperty "Binary uniqness: namespace" (uniqnessEncoding @Namespace),
-        testProperty "Binary uniqness: element name" (uniqnessEncoding @ElementName),
-        testProperty "Binary uniqness: type selector" (uniqnessEncoding @TypeSelector),
-        testProperty "Binary uniqness: attribute" (uniqnessEncoding @Attrib),
-        testProperty "Binary uniqness: attribute name" (uniqnessEncoding @AttributeName),
-        testProperty "Binary uniqness: class" (uniqnessEncoding @Class),
-        testProperty "Binary uniqness: hash" (uniqnessEncoding @Hash)
+        testProperty "Binary uniqness: selector group" (uniqnessEncoding @SelectorGroup)
+      , testProperty "Binary uniqness: selector" (uniqnessEncoding @Selector)
+      , testProperty "Binary uniqness: selector sequence" (uniqnessEncoding @SelectorSequence)
+      , testProperty "Binary uniqness: selector filter" (uniqnessEncoding @SelectorFilter)
+      , testProperty "Binary uniqness: namespace" (uniqnessEncoding @Namespace)
+      , testProperty "Binary uniqness: element name" (uniqnessEncoding @ElementName)
+      , testProperty "Binary uniqness: type selector" (uniqnessEncoding @TypeSelector)
+      , testProperty "Binary uniqness: attribute" (uniqnessEncoding @Attrib)
+      , testProperty "Binary uniqness: attribute name" (uniqnessEncoding @AttributeName)
+      , testProperty "Binary uniqness: class" (uniqnessEncoding @Class)
+      , testProperty "Binary uniqness: hash" (uniqnessEncoding @Hash)
+      , testProperty "Binary uniqness: pseudo class" (uniqnessEncoding @PseudoClass)
+      , testProperty "Binary uniqness: pseudo element" (uniqnessEncoding @PseudoElement)
+      , testProperty "Binary uniqness: pseudo selector sequence" (uniqnessEncoding @PseudoSelectorSequence)
+      , testProperty "Binary uniqness: nth" (uniqnessEncoding @Nth)
+      , testProperty "Binary uniqness: negation" (uniqnessEncoding @Negation)
     ],
     testGroup "Check hash constraint for the Hashable instances" [
-        testProperty "Different hash implies different items: selector group" (hashingDifferent @SelectorGroup),
-        testProperty "Different hash implies different items: selector" (hashingDifferent @Selector),
-        testProperty "Different hash implies different items: selector sequence" (hashingDifferent @SelectorSequence),
-        testProperty "Different hash implies different items: selector filter" (hashingDifferent @SelectorFilter),
-        testProperty "Different hash implies different items: namespace" (hashingDifferent @Namespace),
-        testProperty "Different hash implies different items: element name" (hashingDifferent @ElementName),
-        testProperty "Different hash implies different items: type selector" (hashingDifferent @TypeSelector),
-        testProperty "Different hash implies different items: attribute" (hashingDifferent @Attrib),
-        testProperty "Different hash implies different items: attribute name" (hashingDifferent @AttributeName),
-        testProperty "Different hash implies different items: class" (hashingDifferent @Class),
-        testProperty "Different hash implies different items: hash" (hashingDifferent @Hash)
-    ]
+        testProperty "Different hash implies different items: selector group" (hashingDifferent @SelectorGroup)
+      , testProperty "Different hash implies different items: selector" (hashingDifferent @Selector)
+      , testProperty "Different hash implies different items: selector sequence" (hashingDifferent @SelectorSequence)
+      , testProperty "Different hash implies different items: selector filter" (hashingDifferent @SelectorFilter)
+      , testProperty "Different hash implies different items: namespace" (hashingDifferent @Namespace)
+      , testProperty "Different hash implies different items: element name" (hashingDifferent @ElementName)
+      , testProperty "Different hash implies different items: type selector" (hashingDifferent @TypeSelector)
+      , testProperty "Different hash implies different items: attribute" (hashingDifferent @Attrib)
+      , testProperty "Different hash implies different items: attribute name" (hashingDifferent @AttributeName)
+      , testProperty "Different hash implies different items: class" (hashingDifferent @Class)
+      , testProperty "Different hash implies different items: hash" (hashingDifferent @Hash)
+      , testProperty "Different hash implies different items: pseudo class" (hashingDifferent @PseudoClass)
+      , testProperty "Different hash implies different items: pseudo element" (hashingDifferent @PseudoElement)
+      , testProperty "Different hash implies different items: pseudo selector sequence" (hashingDifferent @PseudoSelectorSequence)
+      , testProperty "Different hash implies different items: nth" (hashingDifferent @Nth)
+      , testProperty "Different hash implies different items: negation" (hashingDifferent @Negation)
+    ],
+    testGroup "Nths" [
+        testProperty "Produces only (strictly) positive values" positiveNth
+      , testProperty "Normalizing produces the same list" normSameNth
+      , testProperty "Normalizing is idempotent" normalizeNthIdempotent
+      , testProperty "Different normalized Nths have different values" (withMaxSuccess 5000 differentNormalizedNthsAreDifferent)
+      , testProperty "nthIsEmpty checks" (withMaxSuccess 5000 checkIfNthIsEmpty)
+      , testProperty "nthContainsValue contains all values" nthContainsSameItems
+      , testProperty "nth contains same as its normalized counterpart" (withMaxSuccess 5000 normalizeContainsSame)
+    ],
+    testGroup "Parse examples" (map (\x -> testProperty ("test CSS selector " ++ x) (checkParse x)) validSelectors)
   ]
 
+-- Based on the w3c testkit: https://test.csswg.org/harness/suite/selectors-3_dev/
+validSelectors :: [String]
+validSelectors = [
+    "body > p"
+  , "div ol>li p"
+  , "*.pastoral"
+  , ".pastoral"
+  , "h1.pastoral"
+  , "p.pastoral.marine"
+  , "h1#chapter1"
+  , "#chapter1"
+  , "*#z98y"
+  , "math + p"
+  , "h1.opener + h2"
+  , "h1 ~ pre"
+  , "*"
+  , "div :first-child"
+  , "div *:first-child"
+  , "body > h2:nth-of-type(n+2):nth-last-of-type(n+2)"
+  , "body > h2:not(:first-of-type):not(:last-of-type)"
+  , "h1, h2, h3"
+  , "h1"
+  , "foo|h1"
+  , "foo|*"
+  , "|h1"
+  , "*|h1"
+  , "*[hreflang|=en]"
+  , "[hreflang|=en]"
+  , "*.warning"
+  , ".warning"
+  , "*#myid"
+  , "#myid"
+  , "ns|*"
+  , "*|*"
+  , "|*"
+  , "*"
+  , "[att]"
+  , "[att=val]"
+  , "[att~=val]"
+  , "[att|=val]"
+  , "h1[title]"
+  , "span[class=\"example\"]"
+  , "span[hello=\"Cleveland\"][goodbye=\"Columbus\"]"
+  , "a[rel~=\"copyright\"]"
+  , "a[href=\"http://www.w3.org/\"]"
+  , "a[hreflang=fr]"
+  , "a[hreflang|=\"en\"]"
+  , "DIALOGUE[character=romeo]"
+  , "DIALOGUE[character=juliet]"
+  , "[att^=val]"
+  , "[att$=val]"
+  , "[att*=val]"
+  , "object[type^=\"image/\"]"
+  , "a[href$=\".html\"]"
+  , "p[title*=\"hello\"]"
+  , "[foo|att=val]"
+  , "[*|att]"
+  , "[|att]"
+  , "[att]"
+  , "EXAMPLE[radix=decimal]"
+  , "EXAMPLE[radix=octal]"
+  , "EXAMPLE"
+  , "*.pastoral"
+  , ".pastoral"
+  , "H1.pastoral"
+  , "p.pastoral.marine"
+  , "h1#chapter1"
+  , "#chapter1"
+  , "*#z98y"
+  , "a.external:visited"
+  , "a:link"
+  , "a:visited"
+  , "a:hover"
+  , "a:active"
+  , "a:focus"
+  , "a:focus:hover"
+  , "p.note:target"
+  , "*:target"
+  , "*:target::before"
+  , "html:lang(fr-be)"
+  , "html:lang(de)"
+  , ":lang(fr-be) > q"
+  , ":lang(de) > q"
+  , "[lang|=fr]"
+  , ":lang(fr)"
+  , "[lang|=fr]"
+  , "tr:nth-child(2n+1)"
+  , "tr:nth-child(odd)"
+  , "tr:nth-child(2n+0)"
+  , "tr:nth-child(even)"
+  , "p:nth-child(4n+1)"
+  , "p:nth-child(4n+2)"
+  , "p:nth-child(4n+3)"
+  , "p:nth-child(4n+4)"
+  , ":nth-child(10n-1)"
+  , ":nth-child(10n+9)"
+  , "foo:nth-child(0n+5)"
+  , "foo:nth-child(5)"
+  , "p"
+  , "p::first-letter"
+  , "span"
+  , "h1 em"
+  , "div * p"
+  , "div p *[href]"
+  , "body > p"
+  , "div ol>li p"
+  , "match + p"
+  , "h1.opener + h2"
+  , "h1 ~ pre"
+  , "*"
+  , "LI"
+  , "UL LI"
+  , "UL OL+LI"
+  , "H1 + *[REL=up]"
+  , "UL OL LI.red"
+  , "LI.red.level"
+  , "#x34y"
+  , "#s12:not(FOO)"
+  , "*"
+  , "E"
+  , "E[foo]"
+  , "E[foo=\"bar\"]"
+  , "E[foo~=\"bar\"]"
+  , "E[foo^=\"bar\"]"
+  , "E[foo$=\"bar\"]"
+  , "E[foo*=\"bar\"]"
+  , "E[foo|=\"en\"]"
+  , "E:root"
+  , "E:nth-child(n)"
+  , "E:nth-last-child(n)"
+  , "E:nth-of-type(n)"
+  , "E:nth-last-of-type(n)"
+  , "E:first-child"
+  , "E:last-child"
+  , "E:first-of-type"
+  , "E:last-of-type"
+  , "E:only-child"
+  , "E:only-of-type"
+  , "E:empty"
+  , "E:link"
+  , "E:visited"
+  , "E:active"
+  , "E:hover"
+  , "E:focus"
+  , "E:target"
+  , "E:lang(fr)"
+  , "E:enabled"
+  , "E:disabled"
+  , "E:checked"
+  , "E::first-line"
+  , "E::first-letter"
+  , "E::before"
+  , "E::after"
+  , "E.warning"
+  , "E#myid"
+  , "E:not(s)"
+  , "E F"
+  , "E > F"
+  , "E + F"
+  , "E ~ F"
+  , ".class"
+  , ".class1.class2"
+  , ".class1 .class2"
+  , "#id"
+  , "*"
+  , "element"
+  , "element.class"
+  , "element,element"
+  , "element element"
+  , "element>element"
+  , "element+element"
+  , "element1~element2"
+  , "[attribute]"
+  , "[attribute=value]"
+  , "[attribute~=value]"
+  , "[attribute|=value]"
+  , "[attribute^=value]"
+  , "[attribute$=value]"
+  , "[attribute*=value]"
+  , ":active"
+  , "::after"
+  , "::before"
+  , ":checked"
+  , ":default"
+  , ":disabled"
+  , ":empty"
+  , ":enabled"
+  , ":first-child"
+  , "::first-letter"
+  , "::first-line"
+  , ":first-of-type"
+  , ":focus"
+  , ":fullscreen"
+  , ":hover"
+  , ":in-range"
+  , ":indeterminate"
+  , ":invalid"
+  , ":lang(language)"
+  , ":last-child"
+  , ":last-of-type"
+  , ":link"
+  , "::marker"
+  , ":not(selector)"
+  , ":nth-child(n)"
+  , ":nth-last-child(n)"
+  , ":nth-last-of-type(n)"
+  , ":nth-of-type(n)"
+  , ":only-of-type"
+  , ":only-child"
+  , ":optional"
+  , ":out-of-range"
+  , "::placeholder"
+  , ":read-only"
+  , ":read-write"
+  , ":required"
+  , ":root"
+  , "::selection"
+  , ":target"
+  , ":valid"
+  , ":visited"
+  ]
+
+checkParse :: String -> Bool
+checkParse x = y == y
+  where y = parseCss x
+
+nthContainsSameItems :: Nth -> Bool
+nthContainsSameItems nth = all (nthContainsValue nth) (take 5000 (nthValues nth))
+
+normalizeContainsSame :: Nth -> Bool
+normalizeContainsSame nth = all (\x -> nthContainsValue nth x == nthContainsValue nnth x) [0 .. 2000]
+    where nnth = normalizeNth nth
+
+equivalentNths :: [(Nth, Nth)]
+equivalentNths = [
+    (Nth 2 1, Odd)
+  , (Nth 2 0, Even)
+  , (Nth 10 (-1), Nth 10 9)
+  ]
+
+checkIfNthIsEmpty :: Nth -> Bool
+checkIfNthIsEmpty nth = nthIsEmpty nth == null (nthValues nth)
+
+positiveNth :: Nth -> Bool
+positiveNth = all (0 <) . take 5000 . nthValues
+
+normSameNth :: Nth -> Bool
+normSameNth n = take 5000 (nthValues n) == take 5000 (nthValues (normalizeNth n))
+
+normalizeNthIdempotent :: Nth -> Bool
+normalizeNthIdempotent x = nx == normalizeNth nx where nx = normalizeNth x
+
+differentNormalizedNthsAreDifferent :: Nth -> Nth -> Property
+differentNormalizedNthsAreDifferent n1 n2 = within 1000000 (nn1 == nn2 || nthValues nn1 /= nthValues nn2)
+    where nn1 = normalizeNth n1
+          nn2 = normalizeNth n2
+
 encodeDecode :: Char -> String -> Bool
 encodeDecode c b = readCssString (encodeString c b) == b
 
@@ -96,16 +386,16 @@
 encodeDecodeCss :: SelectorGroup -> Bool
 encodeDecodeCss sg = sg == (parseCss . unpack . toCssSelector) sg
 
-binaryEquivalent :: (Binary a, Eq a, ToCssSelector a) => a -> Bool
+binaryEquivalent :: (Binary a, Eq a) => a -> Bool
 binaryEquivalent x = decode (encode x) == x
 
 hashingDifferent :: (Hashable a, Eq a) => Int -> a -> a -> Bool
 hashingDifferent slt xa xb = (hashWithSalt slt xa == hashWithSalt slt xb) || (xa /= xb)
 
-uniqnessEncoding :: (Binary a, Eq a, ToCssSelector a) => a -> a -> Bool
+uniqnessEncoding :: (Binary a, Eq a) => a -> a -> Bool
 uniqnessEncoding ca cb = (encode ca == encode cb) == (ca == cb)
 
-encodeDecodeCss' :: ToCssSelector a => a -> Bool
+encodeDecodeCss' :: (Show a, ToCssSelector a) => a -> Bool
 encodeDecodeCss' sg = (parseCss . unpack . toCssSelector . toSelectorGroup) sg == toSelectorGroup sg
 
 buildPattern1 :: SelectorGroup -> Bool