# File lib/asciidoctor/parser.rb, line 1653
  def self.setext_section_title? line1, line2
    if (level = SETEXT_SECTION_LEVELS[line2_ch1 = line2.chr]) &&
        line2_ch1 * (line2_len = line2.length) == line2 && SetextSectionTitleRx.match?(line1) &&
        (line_length(line1) - line2_len).abs < 2
      level
    end
  end