REGEXP_FILE
  RegExpPatternImpl: <(?x)a\ b\ c>
    RegExpBranchImpl: <(?x)a\ b\ c>
      RegExpSetOptionsImpl: <(?x)>
        PsiElement(SET_OPTIONS)('(?')
        RegExpOptionsImpl: <x>
          PsiElement(OPTIONS_ON)('x')
        PsiElement(GROUP_END)(')')
      RegExpCharImpl: <a>
        PsiElement(CHARACTER)('a')
      RegExpCharImpl: <\ >
        PsiElement(ESC_CTRL_CHARACTER)('\ ')
      RegExpCharImpl: <b>
        PsiElement(CHARACTER)('b')
      RegExpCharImpl: <\ >
        PsiElement(ESC_CTRL_CHARACTER)('\ ')
      RegExpCharImpl: <c>
        PsiElement(CHARACTER)('c')