class Kramdown::Parser::Kramdown

def parse_emphasis
  result = @src.scan(EMPHASIS_START)
  element = (result.length == 2 ? :strong : :em)
  type = result[0..0]
  reset_pos = @src.pos
  if (type == '_' && @src.pre_match =~ /[[:alpha:]]\z/ && @src.check(/[[:alpha:]]/)) || @src.check(/\s/) ||
      @tree.type == element || @stack.any? {|el, _| el.type == element}
    add_text(result)
    return
  end
  sub_parse = lambda do |delim, elem|
    el = Element.new(elem)
    stop_re = /#{Regexp.escape(delim)}/
    found = parse_spans(el, stop_re) do
      (@src.pre_match[-1, 1] !~ /\s/) &&
        (elem != :em || !@src.match?(/#{Regexp.escape(delim*2)}(?!#{Regexp.escape(delim)})/)) &&
        (type != '_' || !@src.match?(/#{Regexp.escape(delim)}[[:alpha:]]/)) && el.children.size > 0
    end
    [found, el, stop_re]
  end
  found, el, stop_re = sub_parse.call(result, element)
  if !found && element == :strong && @tree.type != :em
    @src.pos = reset_pos - 1
    found, el, stop_re = sub_parse.call(type, :em)
  end
  if found
    @src.scan(stop_re)
    @tree.children << el
  else
    @src.pos = reset_pos
    add_text(result)
  end
end