def span_descendents(e)
      descendents = []
      e.each_element do |c|
        name = c.respond_to?(:name) ? c.name : nil
        if name && HTML_INLINE_ELEMS.include?(c.name)
          descendents << c
          descendents += span_descendents(c)
        end
      end
    end
def span_descendents(e)
      descendents = []
      e.each_element do |c|
        name = c.respond_to?(:name) ? c.name : nil
        if name && HTML_INLINE_ELEMS.include?(c.name)
          descendents << c
          descendents += span_descendents(c)
        end
      end
    end
Get all span-level descendents of the given element, recursively,
 as an Array.

 @param e [REXML::Element] An element.
 @return [Array]