texmath-0.13.1.2: test/reader/tex/substack.test

<<< tex
\sum_{\substack{
   0<i<m \\
   0<j<n
  }}
 P(i,j)

>>> native
[ EUnder
    True
    (ESymbol Op "\8721")
    (EArray
       [ AlignCenter ]
       [ [ [ EGrouped
               [ ENumber "0"
               , ESymbol Rel "<"
               , EIdentifier "i"
               , ESymbol Rel "<"
               , EIdentifier "m"
               ]
           ]
         ]
       , [ [ EGrouped
               [ ENumber "0"
               , ESymbol Rel "<"
               , EIdentifier "j"
               , ESymbol Rel "<"
               , EIdentifier "n"
               ]
           ]
         ]
       ])
, EIdentifier "P"
, ESymbol Open "("
, EIdentifier "i"
, ESymbol Pun ","
, EIdentifier "j"
, ESymbol Close ")"
]