def tokenize_heredoc_delimiter
      offset = 2
      if cchar == '-'
        advance
        offset = 3
      end

      if cchar =~ /[A-Za-z_]/
        advance
        advance until /[A-Za-z0-9_]/.match( cchar ).nil?
      elsif /['"`]/.match(cchar)
        advance_through_quoted_delimiter(cchar)
      else
        return nil
      end
      @heredoc_delimiter = thunk[offset..-1]
      capture_token( :heredoc_delimiter )
    end
def tokenize_heredoc_delimiter
      offset = 2
      if cchar == '-'
        advance
        offset = 3
      end

      if cchar =~ /[A-Za-z_]/
        advance
        advance until /[A-Za-z0-9_]/.match( cchar ).nil?
      elsif /['"`]/.match(cchar)
        advance_through_quoted_delimiter(cchar)
      else
        return nil
      end
      @heredoc_delimiter = thunk[offset..-1]
      capture_token( :heredoc_delimiter )
    end
Called from tokenize_lt_operators when it identifies that
 << is a heredoc delimiter. Expects that '<<' will already
 be included in the current thunk.