module Hpricot::Builder

def self.set(option, value) 

def self.set(option, value)
  @@default[option] = value
end

def build(*a, &b) 

def build(*a, &b)
  Hpricot.build(*a, &b)
end

def doctype(target, pub, sys) 

def doctype(target, pub, sys)
  @children << DocType.new(target, pub, sys)
end

def head(*args, &block)

set to text/html; charset=utf-8.
Builds a head tag. Adds a meta tag inside with Content-Type 
def head(*args, &block)
  tag!(:head, *args) do
    tag!(:meta, "http-equiv" => "Content-Type", "content" => "text/html; charset=utf-8") if @output_meta_tag
    instance_eval(&block)
  end
end

def html_tag(sym, *args, &block)

could lead to invalid XHTML.
If the @auto_validation setting is on, this method will check for many common mistakes which

for this method.
to calling html_tag(:div). All HTML tags in Hpricot's list are given generated wrappers
Every HTML tag method goes through an html_tag call. So, calling div is equivalent 
def html_tag(sym, *args, &block)
  if @auto_validation and @tagset.self_closing.include?(sym) and block
    raise InvalidXhtmlError, "the `#{sym}' element is self-closing, please remove the block"
  elsif args.empty? and block.nil?
    CssProxy.new(self, sym)
  else
    tag!(sym, *args, &block)
  end
end

def tag!(tag, *args, &block)

the arguments are the same as the tags implemented via method_missing.
Create a tag named +tag+. Other than the first argument which is the tag name, 
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
  f = Elem.new(STag.new(tag, attrs), childs, ETag.new(tag))
  # build children from the block
  if block
    build(f, &block)
  end
  @children << f
  f
end

def text(string)

Write a +string+ to the HTML stream without escaping it. 
def text(string)
  @children << Text.new(string)
  nil
end

def text!(string)

Write a +string+ to the HTML stream, making sure to escape it. 
def text!(string)
  @children << Text.new(string.fast_xs)
end

def xhtml_html(attrs = {}, &block) 

def xhtml_html(attrs = {}, &block)
  instruct! if @output_xml_instruction
  doctype(:html, *@@default[:tagset].doctype)
  tag!(:html, @@default[:root_attributes].merge(attrs), &block)
end

def xhtml_strict(attrs = {}, &block)

Builds an html tag with XHTML 1.0 Strict doctype instead. 
def xhtml_strict(attrs = {}, &block)
  # self.tagset = Hpricot::XHTMLStrict
  xhtml_html(attrs, &block)
end

def xhtml_transitional(attrs = {}, &block)

:lang => "en".
are prepended. Also assumes :xmlns => "http://www.w3.org/1999/xhtml",
Builds an html tag. An XML 1.0 instruction and an XHTML 1.0 Transitional doctype 
def xhtml_transitional(attrs = {}, &block)
  # self.tagset = Hpricot::XHTMLTransitional
  xhtml_html(attrs, &block)
end