isExpression:
   'is' '(' type identifier? ')'
   'is' '(' type identifier? ':' typeSpecialization ')'
   'is' '(' type identifier? '=' typeSpecialization ')'
   'is' '(' type identifier? ':' typeSpecialization ',' templateParameterList ')'
   'is' '(' type identifier? '=' typeSpecialization ',' templateParameterList ')'
   ;