def span_descendents(e)
      ns = Nokogiri::XML::NodeSet.new(Nokogiri::XML::Document.new)
      e.element_children.inject(ns) do |descendents, c|
        if HTML_INLINE_ELEMS.include?(c.name)
          descendents << c
          descendents += span_descendents(c)
        end
        descendents
      end
    end
def span_descendents(e)
      ns = Nokogiri::XML::NodeSet.new(Nokogiri::XML::Document.new)
      e.element_children.inject(ns) do |descendents, c|
        if HTML_INLINE_ELEMS.include?(c.name)
          descendents << c
          descendents += span_descendents(c)
        end
        descendents
      end
    end
Get all span-level descendents of the given element, recursively,
 as a flat NodeSet.

 @param e [Nokogiri::XML::Node] An element.
 @return [Nokogiri::XML::NodeSet]