---
string
  string_start
    STRING_START "`" (1, 1)
  str_content
    str_content
      str_content
        str_content
          str_content
            str_content
            str
              STR "a" (1, 2)
          var
            VAR "b" (1, 6)
        str
          STR "c" (1, 9)
      var
        VAR "d" (1, 13)
    str
      STR "e" (1, 16)
  string_end
    STRING_END "`" (1, 17)