def namespace_bindings_from_defs(ns_defs)
      (ns_defs||[]).reduce({}) do |h,ns_def|
        h[ns_def.prefix||""] = ns_def.href
        h
      end
    end
def namespace_bindings_from_defs(ns_defs)
      (ns_defs||[]).reduce({}) do |h,ns_def|
        h[ns_def.prefix||""] = ns_def.href
        h
      end
    end
give a list of <tt>Nokogiri::XML::Namespace</tt> definitions, produce
 a Hash <tt>{prefix=>uri}</tt> of namespace bindings