module Hpricot::Builder

def tag!(tag, *args, &block)
  ele_id = nil
  if @auto_validation and @tagset
      if !@tagset.tagset.has_key?(tag)
          raise InvalidXhtmlError, "no element `#{tag}' for #{tagset.doctype}"
      elsif args.last.respond_to?(:to_hash)
          attrs = args.last.to_hash
          if @tagset.forms.include?(tag) and attrs[:id]
            attrs[:name] ||= attrs[:id]
          end
          attrs.each do |k, v|
              atname = k.to_s.downcase.intern
              unless k =~ /:/ or @tagset.tagset[tag].include? atname
                  raise InvalidXhtmlError, "no attribute `#{k}' on #{tag} elements"
              end
              if atname == :id
                  ele_id = v.to_s
                  if @elements.has_key? ele_id
                      raise InvalidXhtmlError, "id `#{ele_id}' already used (id's must be unique)."
                  end
              end
          end
      end
  end
  # turn arguments into children or attributes
  childs = []
  attrs = args.grep(Hash)
  childs.concat((args - attrs).flatten.map do |x|
    if x.respond_to? :to_html
      Hpricot.make(x.to_html)
    elsif x
      Text.new(x.fast_xs)
    end
  end.flatten)
  attrs = attrs.inject({}) do |hsh, ath|
    ath.each do |k, v|
      hsh[k] = v.to_s.fast_xs if v
    end
    hsh
  end
  # create the element itself
  tag = tag.to_s
  f = Elem.new(tag, attrs, childs, ETag.new(tag))
  # build children from the block
  if block
    build(f, &block)
  end
  add_child f
  f
end