REGEXP_FILE
  RegExpPatternImpl: <^abc$>
    RegExpBranchImpl: <^abc$>
      RegExpBoundaryImpl: <^>
        PsiElement(CARET)('^')
      RegExpCharImpl: <a>
        PsiElement(CHARACTER)('a')
      RegExpCharImpl: <b>
        PsiElement(CHARACTER)('b')
      RegExpCharImpl: <c>
        PsiElement(CHARACTER)('c')
      RegExpBoundaryImpl: <$>
        PsiElement(DOLLAR)('$')