def header_style(header)
      if header.type != :header
        raise "header_style called with non-header element"
      end
      line = element_line(header)
      if line.start_with?("#")
        if line.strip.end_with?("#")
          :atx_closed
        else
          :atx
        end
      else
        :setext
      end
    end
def header_style(header)
      if header.type != :header
        raise "header_style called with non-header element"
      end
      line = element_line(header)
      if line.start_with?("#")
        if line.strip.end_with?("#")
          :atx_closed
        else
          :atx
        end
      else
        :setext
      end
    end
Returns the header 'style' - :atx (hashes at the beginning), :atx_closed
 (atx header style, but with hashes at the end of the line also), :setext
 (underlined). You can pass in the element object or an options hash
 here.