pandoc-3.10: test/command/11589.md

```
% pandoc -f markdown -t native
t^[a]{.cb}\ b^
t^[a]{fg=yellow bg=blue}\ b^
^D
[ Para
    [ Str "t"
    , Superscript
        [ Span ( "" , [ "cb" ] , [] ) [ Str "a" ] , Str "\160b" ]
    , SoftBreak
    , Str "t"
    , Superscript
        [ Span
            ( "" , [] , [ ( "fg" , "yellow" ) , ( "bg" , "blue" ) ] )
            [ Str "a" ]
        , Str "\160b"
        ]
    ]
]
```