ruby--ruby/lib/rexml/element.rb

require "rexml/parent"
require "rexml/namespace"
require "rexml/attribute"
require "rexml/cdata"
require "rexml/xpath"
require "rexml/parseexception"

module REXML
	# Represents a tagged XML element.  Elements are characterized by
	# having children, attributes, and names, and can themselves be
	# children.
	class Element < Parent
		include Namespace

		UNDEFINED = "UNDEFINED";		# The default name

		# Mechanisms for accessing attributes and child elements of this
		# element.
		attr_reader :attributes, :elements
		# The context holds information about the processing environment, such as
		# whitespace handling.
		attr_accessor :context

		# Constructor
		# arg:: 
		# 	if not supplied, will be set to the default value.
		# 	If a String, the name of this object will be set to the argument.
		# 	If an Element, the object will be shallowly cloned; name, 
		# 	attributes, and namespaces will be copied.  Children will +not+ be
		# 	copied.
		# 	If a Source, the source will be scanned and parsed for an Element,
		# 	and all child elements will be recursively parsed as well.
		# parent:: 
		# 	if supplied, must be a Parent, and will be used as
		# 	the parent of this object.
		# context::
		# 	If supplied, must be a hash containing context items.  Context items
		# 	include:
		# * <tt>:respect_whitespace</tt> the value of this is :+all+ or an array of
		#   strings being the names of the elements to respect
		#   whitespace for.  Defaults to :+all+.
		# * <tt>:compress_whitespace</tt> the value can be :+all+ or an array of
		#   strings being the names of the elements to ignore whitespace on.
		#   Overrides :+respect_whitespace+.
		# * <tt>:ignore_whitespace_nodes</tt> the value can be :+all+ or an array
		#   of strings being the names of the elements in which to ignore
		#   whitespace-only nodes.  If this is set, Text nodes which contain only
		#   whitespace will not be added to the document tree.
		# * <tt>:raw</tt> can be :+all+, or an array of strings being the names of
		#   the elements to process in raw mode.  In raw mode, special
		#   characters in text is not converted to or from entities.
		def initialize( arg = UNDEFINED, parent=nil, context=nil )
			super(parent)

			@elements = Elements.new self
			@attributes = Attributes.new self
			@context = context

			if arg.kind_of? String
				self.name = arg
			elsif arg.kind_of? Element
				self.name = arg.expanded_name
				arg.attributes.each_attribute{ |attribute|
					@attributes << Attribute.new( attribute )
				}
				@context = arg.context
			end
		end

		# Creates a shallow copy of self.
		#   d = Document.new "<a><b/><b/><c><d/></c></a>"
		#   new_a = d.root.clone
		#   puts new_a  # => "<a/>"
		def clone
			Element.new self
		end

		# Evaluates to the root element of the document that this element 
		# belongs to. If this element doesn't belong to a document, but does
		# belong to another Element, the parent's root will be returned, until the
		# earliest ancestor is found.
		#  d = Document.new '<a><b><c/></b></a>'
		#  a = d[1] ; c = a[1][1]
		#  d.root        # These all evaluate to the same Element,
		#  a.root        # namely, <a>
		#  c.root        #
		def root
			parent.nil? ? self : parent.root
		end

		# Evaluates to the document to which this element belongs, or nil if this
		# element doesn't belong to a document.
		def document
			root.parent if root
		end

		# Evaluates to +true+ if whitespace is respected for this element.  This
		# is the case if:
		# 1. Neither :+respect_whitespace+ nor :+compress_whitespace+ has any value
		# 2. The context has :+respect_whitespace+ set to :+all+ or
		#    an array containing the name of this element, and :+compress_whitespace+
		#    isn't set to :+all+ or an array containing the name of this element.
		# The evaluation is tested against +expanded_name+, and so is namespace
		# sensitive.
		def whitespace
			@whitespace = nil
			if @context
				if @context[:respect_whitespace]
					@whitespace = (@context[:respect_whitespace] == :all or
												 @context[:respect_whitespace].include? expanded_name)
				end
				@whitespace = false if (@context[:compress_whitespace] and
					(@context[:compress_whitespace] == :all or
					 @context[:compress_whitespace].include? expanded_name)
				)
			end
			@whitespace = true unless @whitespace == false
			@whitespace
		end

		def ignore_whitespace_nodes
			@ignore_whitespace_nodes = false
			if @context
				if @context[:ignore_whitespace_nodes]
					@ignore_whitespace_nodes = 
						(@context[:ignore_whitespace_nodes] == :all or
						 @context[:ignore_whitespace_nodes].include? expanded_name)
				end
			end
		end

		# Evaluates to +true+ if raw mode is set for this element.  This
		# is the case if the context has :+raw+ set to :+all+ or
		# an array containing the name of this element.
		#
		# The evaluation is tested against +expanded_name+, and so is namespace
		# sensitive.
		def raw
			@raw = (@context and @context[:raw] and
			(@context[:raw] == :all or
			@context[:raw].include? expanded_name))
			@raw
		end

		#once :whitespace, :raw, :ignore_whitespace_nodes

		#################################################
		# Namespaces                                    #
		#################################################

		# Evaluates to an +Array+ containing the prefixes (names) of all defined
		# namespaces at this context node.
		#  doc = Document.new("<a xmlns:x='1' xmlns:y='2'><b/><c xmlns:z='3'/></a>")
		#  doc.elements['//b'].prefixes # -> ['x', 'y']
		def prefixes
			prefixes = []
			prefixes = parent.prefixes if parent
			prefixes |= attributes.prefixes
			return prefixes
		end

		def namespaces
			namespaces = []
			namespaces = parent.namespaces if parent
			namespaces |= attributes.namespaces
			return namespaces
		end

		# Evalutas to the URI for a prefix, or the empty string if no such 
		# namespace is declared for this element. Evaluates recursively for
		# ancestors.  Returns the default namespace, if there is one.
		# prefix:: 
		#   the prefix to search for.  If not supplied, returns the default
		#   namespace if one exists
		# Returns:: 
		#   the namespace URI as a String, or nil if no such namespace
		#   exists.  If the namespace is undefined, returns an empty string
		#  doc = Document.new("<a xmlns='1' xmlns:y='2'><b/><c xmlns:z='3'/></a>")
		#  b = doc.elements['//b']
		#  b.namespace           # -> '1'
		#  b.namespace("y")      # -> '2'
		def namespace(prefix=nil)
			if prefix.nil?
				prefix = prefix()
			end
			if prefix == ''
				prefix = "xmlns"
			else
				prefix = "xmlns:#{prefix}" unless prefix[0,5] == 'xmlns'
			end
			ns = attributes[ prefix ]
			ns = parent.namespace(prefix) if ns.nil? and parent
			ns = '' if ns.nil? and prefix == 'xmlns'
			return ns
		end

		# Adds a namespace to this element.
		# prefix:: 
		#   the prefix string, or the namespace URI if +uri+ is not
		#   supplied
		# uri::    
		#   the namespace URI.  May be nil, in which +prefix+ is used as
		#   the URI
		# Evaluates to: this Element
		#  a = Element.new("a")
		#  a.add_namespace("xmlns:foo", "bar" )
		#  a.add_namespace("foo", "bar")  # shorthand for previous line
		#  a.add_namespace("twiddle")
		#  puts a   #-> <a xmlns:foo='bar' xmlns='twiddle'/>
		def add_namespace( prefix, uri=nil )
			unless uri
				@attributes["xmlns"] = prefix
			else
				prefix = "xmlns:#{prefix}" unless prefix =~ /^xmlns:/
				@attributes[ prefix ] = uri
			end
			self
		end

		# Removes a namespace from this node.  This only works if the namespace is
		# actually declared in this node.  If no argument is passed, deletes the
		# default namespace.
		#
		# Evaluates to: this element
		#  doc = Document.new "<a xmlns:foo='bar' xmlns='twiddle'/>"
		#  doc.root.delete_namespace
		#  puts doc     # -> <a xmlns:foo='bar'/>
		#  doc.root.delete_namespace 'foo'
		#  puts doc     # -> <a/>
		def delete_namespace namespace="xmlns"
			namespace = "xmlns:#{namespace}" unless namespace == 'xmlns'
			attribute = attributes.get_attribute(namespace)
			attribute.remove unless attribute.nil?
			self
		end

		#################################################
		# Elements                                      #
		#################################################

		# Adds a child to this element, optionally setting attributes in
		# the element.
		# element:: 
		#   optional.  If Element, the element is added.
		#   Otherwise, a new Element is constructed with the argument (see
		#   Element.initialize).
		# attrs:: 
		#   If supplied, must be a Hash containing String name,value 
		#   pairs, which will be used to set the attributes of the new Element.
		# Returns:: the Element that was added
		#  el = doc.add_element 'my-tag'
		#  el = doc.add_element 'my-tag', {'attr1'=>'val1', 'attr2'=>'val2'}
		#  el = Element.new 'my-tag'
		#  doc.add_element el
		def add_element element=nil, attrs=nil
			el = @elements.add element
			if attrs.kind_of? Hash
				attrs.each do |key, value|
					el.attributes[key]=value if key =~ /^xmlns:/
				end
				attrs.each do |key, value|
					el.attributes[key]=value if key !~ /^xmlns:/
				end
			end
			el
		end

		# Deletes a child element.
		# element:: 
		#   Must be an +Element+, +String+, or +Integer+.  If Element, 
		#   the element is removed.  If String, the element is found (via XPath) 
		#   and removed.  <em>This means that any parent can remove any
		#   descendant.<em>  If Integer, the Element indexed by that number will be
		#   removed.
		# Returns:: the element that was removed.
		#  doc.delete_element "/a/b/c[@id='4']"
		#  doc.delete_element doc.elements["//k"]
		#  doc.delete_element 1
		def delete_element element
			@elements.delete element
		end

		# Evaluates to +true+ if this element has at least one child Element
		#  doc = Document.new "<a><b/><c>Text</c></a>"
		#  doc.root.has_elements               # -> true
		#  doc.elements["/a/b"].has_elements   # -> false
		#  doc.elements["/a/c"].has_elements   # -> false
		def has_elements?
			!@elements.empty?
		end

		# Iterates through the child elements, yielding for each Element that
		# has a particular attribute set.
		# key:: 
		#   the name of the attribute to search for
		# value:: 
		#   the value of the attribute
		# max:: 
		#   (optional) causes this method to return after yielding 
		#   for this number of matching children
		# name:: 
		#   (optional) if supplied, this is an XPath that filters
		#   the children to check.
		#
		#  doc = Document.new "<a><b @id='1'/><c @id='2'/><d @id='1'/><e/></a>"
		#  # Yields b, c, d
		#  doc.root.each_element_with_attribute( 'id' ) {|e| p e}
		#  # Yields b, d
		#  doc.root.each_element_with_attribute( 'id', '1' ) {|e| p e}
		#  # Yields b
		#  doc.root.each_element_with_attribute( 'id', '1', 1 ) {|e| p e}
		#  # Yields d
		#  doc.root.each_element_with_attribute( 'id', '1', 0, 'd' ) {|e| p e}
		def each_element_with_attribute( key, value=nil, max=0, name=nil, &block ) # :yields: Element
			each_with_something( proc {|child| 
				if value.nil?
					child.attributes[key] != nil
				else
					child.attributes[key]==value
				end
			}, max, name, &block )
		end

		# Iterates through the children, yielding for each Element that
		# has a particular text set.
		# text:: 
		#   the text to search for.  If nil, or not supplied, will itterate
		#   over all +Element+ children that contain at least one +Text+ node.
		# max:: 
		#   (optional) causes this method to return after yielding
		#   for this number of matching children
		# name:: 
		#   (optional) if supplied, this is an XPath that filters
		#   the children to check.
		#
		#  doc = Document.new '<a><b>b</b><c>b</c><d>d</d><e/></a>'
		#  # Yields b, c, d
		#  doc.each_element_with_text {|e|p e}
		#  # Yields b, c
		#  doc.each_element_with_text('b'){|e|p e}
		#  # Yields b
		#  doc.each_element_with_text('b', 1){|e|p e}
		#  # Yields d
		#  doc.each_element_with_text(nil, 0, 'd'){|e|p e}
		def each_element_with_text( text=nil, max=0, name=nil, &block ) # :yields: Element
			each_with_something( proc {|child| 
				if text.nil?
					child.has_text?
				else
					child.text == text
				end
			}, max, name, &block )
		end

		# Synonym for Element.elements.each
		def each_element( xpath=nil, &block ) # :yields: Element
			@elements.each( xpath, &block )
		end

		# Synonym for Element.to_a
		# This is a little slower than calling elements.each directly.
		# xpath:: any XPath by which to search for elements in the tree
		# Returns:: an array of Elements that match the supplied path
		def get_elements( xpath )
			@elements.to_a( xpath )
		end

		# Returns the next sibling that is an element, or nil if there is
		# no Element sibling after this one
		#  doc = Document.new '<a><b/>text<c/></a>'
		#  doc.root.elements['b'].next_element          #-> <c/>
		#  doc.root.elements['c'].next_element          #-> nil
		def next_element
			element = next_sibling
			element = element.next_sibling until element.nil? or element.kind_of? Element 
			return element
		end

		# Returns the previous sibling that is an element, or nil if there is
		# no Element sibling prior to this one
		#  doc = Document.new '<a><b/>text<c/></a>'
		#  doc.root.elements['c'].previous_element          #-> <b/>
		#  doc.root.elements['b'].previous_element          #-> nil
		def previous_element
			element = previous_sibling
			element = element.previous_sibling until element.nil? or element.kind_of? Element
			return element
		end


		#################################################
		# Text                                          #
		#################################################

		# Evaluates to +true+ if this element has at least one Text child
		def has_text?
			not text().nil?
		end

		# A convenience method which returns the String value of the _first_
		# child text element, if one exists, and +nil+ otherwise.
		#
		# <em>Note that an element may have multiple Text elements, perhaps
		# separated by other children</em>.  Be aware that this method only returns
		# the first Text node.
		#
		# This method returns the +value+ of the first text child node, which
		# ignores the +raw+ setting, so always returns normalized text. See
		# the Text::value documentation.
		#
		#  doc = Document.new "<p>some text <b>this is bold!</b> more text</p>"
		#  # The element 'p' has two text elements, "some text " and " more text".
		#  doc.root.text              #-> "some text "
		def text( path = nil )
			rv = get_text path
			return rv.value unless rv.nil?
			nil
		end

		# Returns the first child Text node, if any, or +nil+ otherwise.
		# This method returns the actual +Text+ node, rather than the String content.
		#  doc = Document.new "<p>some text <b>this is bold!</b> more text</p>"
		#  # The element 'p' has two text elements, "some text " and " more text".
		#  doc.root.get_text.value            #-> "some text "
		def get_text path = nil
			rv = nil
			if path
				element = @elements[ path ]
				rv = element.get_text unless element.nil?
			else
				rv = find { |node| node.kind_of? Text }
			end
			return rv
		end

		# Sets the first Text child of this object.  See text() for a
		# discussion about Text children.
		#
		# If a Text child already exists, the child is replaced by this
		# content.  This means that Text content can be deleted by calling
		# this method with a nil argument.  In this case, the next Text
		# child becomes the first Text child.  In no case is the order of
		# any siblings disturbed.
		# text:: 
		#   If a String, a new Text child is created and added to
		#   this Element as the first Text child.  If Text, the text is set
		#   as the first Child element.  If nil, then any existing first Text
		#   child is removed.
		# Returns:: this Element.
		#  doc = Document.new '<a><b/></a>'
		#  doc.root.text = 'Sean'      #-> '<a><b/>Sean</a>'
		#  doc.root.text = 'Elliott'   #-> '<a><b/>Elliott</a>'
		#  doc.root.add_element 'c'    #-> '<a><b/>Elliott<c/></a>'
		#  doc.root.text = 'Russell'   #-> '<a><b/>Russell<c/></a>'
		#  doc.root.text = nil         #-> '<a><b/><c/></a>'
		def text=( text )
			text = Text.new( text, whitespace(), nil, raw() ) if text.kind_of? String
			old_text = get_text
			if text.nil?
				old_text.remove unless old_text.nil?
			else
				if old_text.nil?
					self << text
				else
					old_text.replace_with( text )
				end
			end
			return self
		end

		# A helper method to add a Text child.  Actual Text instances can
		# be added with regular Parent methods, such as add() and <<()
		# text::
		#   if a String, a new Text instance is created and added
		#   to the parent.  If Text, the object is added directly.
		# Returns:: this Element
		#  e = Element.new('a')          #-> <e/>
		#  e.add_text 'foo'              #-> <e>foo</e>
		#  e.add_text Text.new(' bar')    #-> <e>foo bar</e>
		# Note that at the end of this example, the branch has <b>3</b> nodes; the 'e'
		# element and <b>2</b> Text node children.
		def add_text( text )
			if text.kind_of? String 
				if @children[-1].kind_of? Text
					@children[-1] << text
					return
				end
				text = Text.new( text, whitespace(), nil, raw() )
			end
			self << text unless text.nil?
			return self
		end

    def node_type
      :element
    end

		#################################################
		# Attributes                                    #
		#################################################

		def attribute( name, namespace=nil )
			prefix = ''
			if namespace
				prefix = attributes.prefixes.each { |prefix|
					return "#{prefix}:" if namespace( prefix ) == namespace
				} || ''
			end
			attributes.get_attribute( "#{prefix}#{name}" )
		end

		# Evaluates to +true+ if this element has any attributes set, false
		# otherwise.
		def has_attributes?
			return !@attributes.empty?
		end

		# Adds an attribute to this element, overwriting any existing attribute
		# by the same name.
		# key::
		#   can be either an Attribute or a String.  If an Attribute,
		#   the attribute is added to the list of Element attributes.  If String,
		#   the argument is used as the name of the new attribute, and the value
		#   parameter must be supplied.
		# value:: 
		#   Required if +key+ is a String, and ignored if the first argument is
		#   an Attribute.  This is a String, and is used as the value
		#   of the new Attribute.
		# Returns:: the Attribute added
		#  e = Element.new 'e'
		#  e.add_attribute( 'a', 'b' )               #-> <e a='b'/>
		#  e.add_attribute( 'x:a', 'c' )             #-> <e a='b' x:a='c'/>
		#  e.add_attribute Attribute.new('b', 'd')   #-> <e a='b' x:a='c' b='d'/>
		def add_attribute( key, value=nil )
			if key.kind_of? Attribute
				@attributes << key
			else
				@attributes[key] = value
			end
		end

		# Add multiple attributes to this element.
		# hash:: is either a hash, or array of arrays
		#  el.add_attributes( {"name1"=>"value1", "name2"=>"value2"} )
		#  el.add_attributes( [ ["name1","value1"], ["name2"=>"value2"] ] )
		def add_attributes hash
			if hash.kind_of? Hash
				hash.each_pair {|key, value| @attributes[key] = value }
			elsif hash.kind_of? Array
				hash.each { |value| @attributes[ value[0] ] = value[1] }
			end
		end

		# Removes an attribute
		# key::
		#   either an Attribute or a String.  In either case, the
		#   attribute is found by matching the attribute name to the argument,
		#   and then removed.  If no attribute is found, no action is taken.
		# Returns:: 
		#   the attribute removed, or nil if this Element did not contain
		#   a matching attribute
		#  e = Element.new('E')
		#  e.add_attribute( 'name', 'Sean' )             #-> <E name='Sean'/>
		#  r = e.add_attribute( 'sur:name', 'Russell' )  #-> <E name='Sean' sur:name='Russell'/>
		#  e.delete_attribute( 'name' )                  #-> <E sur:name='Russell'/>
		#  e.delete_attribute( r )                       #-> <E/>
		def delete_attribute(key)
			attr = @attributes.get_attribute(key)
			attr.remove unless attr.nil?
		end

		#################################################
		# Other Utilities                               #
		#################################################

		# Get an array of all CData children.  
		# IMMUTABLE
		def cdatas
			find_all { |child| child.kind_of? CData }.freeze
		end

		# Get an array of all Comment children.
		# IMMUTABLE
		def comments
			find_all { |child| child.kind_of? Comment }.freeze
		end

		# Get an array of all Instruction children.
		# IMMUTABLE
		def instructions
			find_all { |child| child.kind_of? Instruction }.freeze
		end

		# Get an array of all Text children.
		# IMMUTABLE
		def texts
			find_all { |child| child.kind_of? Text }.freeze
		end

		# Writes out this element, and recursively, all children.
		# output::
		#	  output an object which supports '<< string'; this is where the
		#   document will be written.
		# indent::
		#   An integer.  If -1, no indenting will be used; otherwise, the
		#   indentation will be this number of spaces, and children will be
		#   indented an additional amount.  Defaults to -1
		# transitive::
		#   What the heck does this do? Defaults to false
		# ie_hack::
		#   Internet Explorer is the worst piece of crap to have ever been
		#   written, with the possible exception of Windows itself.  Since IE is
		#   unable to parse proper XML, we have to provide a hack to generate XML
		#   that IE's limited abilities can handle.  This hack inserts a space 
		#   before the /> on empty tags.  Defaults to false
		#
		#  out = ''
		#  doc.write( out )     #-> doc is written to the string 'out'
		#  doc.write( $stdout ) #-> doc written to the console
		def write(writer=$stdout, indent=-1, transitive=false, ie_hack=false)
			#print "ID:#{indent}"
			writer << "<#@expanded_name"

			@attributes.each_attribute do |attr|
				writer << " "
				attr.write( writer, indent )
			end unless @attributes.empty?

			if @children.empty?
				writer << " " if ie_hack
				writer << "/" 
			else
				if transitive and indent>-1 and !@children[0].kind_of? Text
					writer << "\n"
					indent writer, indent+2
				end
				writer << ">"
				write_children( writer, indent, transitive, ie_hack )
				writer << "</#{expanded_name}"
			end
			if transitive and indent>-1
				writer << "\n"
				indent -= 2 if next_sibling.nil?
				indent(writer, indent)
			end
			writer << ">"
		end


		private
		# A private helper method
		def each_with_something( test, max=0, name=nil )
			num = 0
			child=nil
			@elements.each( name ){ |child|
				yield child if test.call(child) and num += 1
				return if max>0 and num == max
			}
		end

		# A private helper method
		def write_children( writer, indent, transitive, ie_hack )
			cr = (indent < 0) ? '' : "\n"
			#if size == 1 and @children[0].kind_of?(Text)
			#	self[0].write( writer, -1 )
			if indent == -1
				each { |child| child.write( writer, indent, transitive, ie_hack ) }
			else
				next_indent = indent+2
				last_child=nil
				each { |child|
					unless child.kind_of? Text or last_child.kind_of? Text or transitive
						writer << cr
						indent(writer, next_indent)
					end
					child.write( writer, next_indent, transitive, ie_hack )
					last_child = child
				}
				unless last_child.kind_of? Text or transitive
					writer << cr
					indent( writer, indent )
				end
			end
		end
	end

	########################################################################
	# ELEMENTS                                                             #
	########################################################################

	# A class which provides filtering of children for Elements, and
	# XPath search support.  You are expected to only encounter this class as
	# the <tt>element.elements</tt> object.  Therefore, you are 
	# _not_ expected to instantiate this yourself.
	class Elements
		include Enumerable
		# Constructor
		# parent:: the parent Element
		def initialize parent
			@element = parent
		end

		# Fetches a child element.  Filters only Element children, regardless of
		# the XPath match.
		# index:: 
		#   the search parameter.  This is either an Integer, which
		#   will be used to find the index'th child Element, or an XPath,
		#   which will be used to search for the Element.  <em>Because
		#   of the nature of XPath searches, any element in the connected XML
		#   document can be fetched through any other element.</em>  <b>The
		#   Integer index is 1-based, not 0-based.</b>  This means that the first
		#   child element is at index 1, not 0, and the +n+th element is at index
		#   +n+, not <tt>n-1</tt>.  This is because XPath indexes element children
		#   starting from 1, not 0, and the indexes should be the same.
		# name:: 
		#   optional, and only used in the first argument is an
		#   Integer.  In that case, the index'th child Element that has the
		#   supplied name will be returned.  Note again that the indexes start at 1.
		# Returns:: the first matching Element, or nil if no child matched
		#  doc = Document.new '<a><b/><c id="1"/><c id="2"/><d/></a>'
		#  doc.root.elements[1]       #-> <b/>
		#  doc.root.elements['c']     #-> <c id="1"/>
		#  doc.root.elements[2,'c']   #-> <c id="2"/>
		def []( index, name=nil)
			if index.kind_of? Integer
				raise "index (#{index}) must be >= 1" if index < 1
				name = literalize name if name
				num = 0
				child = nil
				@element.find { |child|
					child.kind_of? Element and
					(name.nil? ? true : child.has_name?( name )) and 
					(num += 1) == index
				}
			else
				return XPath::first( @element, index )
				#{ |element| 
				#	return element if element.kind_of? Element
				#}
				#return nil
			end
		end

		# Sets an element, replacing any previous matching element.  If no
		# existing element is found ,the element is added.
		# index:: Used to find a matching element to replace.  See []().
		# element:: 
		#   The element to replace the existing element with
		#   the previous element
		# Returns:: nil if no previous element was found.
		#
		#  doc = Document.new '<a/>'
		#  doc.root.elements[10] = Element.new('b')    #-> <a><b/></a>
		#  doc.root.elements[1]                        #-> <b/>
		#  doc.root.elements[1] = Element.new('c')     #-> <a><c/></a>
		#  doc.root.elements['c'] = Element.new('d')   #-> <a><d/></a>
		def []=( index, element )
			previous = self[index]
			if previous.nil?
				@element.add element
			else
				previous.replace_with element
			end
			return previous
		end

		# Returns +true+ if there are no +Element+ children, +false+ otherwise
		def empty?
			@element.find{ |child| child.kind_of? Element}.nil?
		end

		# Returns the index of the supplied child (starting at 1), or -1 if 
		# the element is not a child
		# element:: an +Element+ child
		def index element
			rv = 0
			found = @element.find do |child| 
				child.kind_of? Element and
				(rv += 1) and
				child == element
			end
			return rv if found == element
			return -1
		end

		# Deletes a child Element
		# element:: 
		#   Either an Element, which is removed directly; an
		#   xpath, where the first matching child is removed; or an Integer,
		#   where the n'th Element is removed.
		# Returns:: the removed child
		#  doc = Document.new '<a><b/><c/><c id="1"/></a>'
		#  b = doc.root.elements[1]
		#  doc.root.elements.delete b           #-> <a><c/><c id="1"/></a>
		#  doc.elements.delete("a/c[@id='1']")  #-> <a><c/></a>
		#  doc.root.elements.delete 1           #-> <a/>
		def delete element
			if element.kind_of? Element
				@element.delete element
			else
				el = self[element]
				el.remove if el
			end
		end

		# Removes multiple elements.  Filters for Element children, regardless of
		# XPath matching.
		# xpath:: all elements matching this String path are removed.
		# Returns:: an Array of Elements that have been removed
		#  doc = Document.new '<a><c/><c/><c/><c/></a>'
		#  deleted = doc.elements.delete_all 'a/c' #-> [<c/>, <c/>, <c/>, <c/>]
		def delete_all( xpath )
			rv = []
			XPath::each( @element, xpath) {|element| 
				rv << element if element.kind_of? Element
			}
			rv.each do |element|
				@element.delete element
				element.remove
			end
			return rv
		end

		# Adds an element
		# element:: 
		#   if supplied, is either an Element, String, or
		#   Source (see Element.initialize).  If not supplied or nil, a
		#   new, default Element will be constructed
		# Returns:: the added Element
		#  a = Element.new 'a'
		#  a.elements.add Element.new 'b'  #-> <a><b/></a>
		#  a.elements.add 'c'              #-> <a><b/><c/></a>
		def add element=nil
			rv = nil
			if element.nil?
				Element.new "", self, @element.context
			elsif not element.kind_of?(Element)
				Element.new element, self, @element.context
			else
				@element << element
				element.context = @element.context
				element
			end
		end

		alias :<< :add

		# Iterates through all of the child Elements, optionally filtering
		# them by a given XPath
		# xpath:: 
		#   optional.  If supplied, this is a String XPath, and is used to 
		#   filter the children, so that only matching children are yielded.  Note
		#   that XPaths are automatically filtered for Elements, so that
		#   non-Element children will not be yielded
		#  doc = Document.new '<a><b/><c/><d/>sean<b/><c/><d/></a>'
		#  doc.root.each {|e|p e}       #-> Yields b, c, d, b, c, d elements
		#  doc.root.each('b') {|e|p e}  #-> Yields b, b elements
		#  doc.root.each('child::node()')  {|e|p e}
		#  #-> Yields <b/>, <c/>, <d/>, <b/>, <c/>, <d/>
		#  XPath.each(doc.root, 'child::node()', &block)
		#  #-> Yields <b/>, <c/>, <d/>, sean, <b/>, <c/>, <d/>
		def each( xpath=nil, &block)
			XPath::each( @element, xpath ) {|e| yield e if e.kind_of? Element }
		end

		# Returns the number of +Element+ children of the parent object.
		#  doc = Document.new '<a>sean<b/>elliott<b/>russell<b/></a>'
		#  doc.root.size            #-> 6, 3 element and 3 text nodes
		#  doc.root.elements.size   #-> 3
		def size
			count = 0
			@element.each {|child| count+=1 if child.kind_of? Element }
			count
		end

		# Returns an Array of Element children.  An XPath may be supplied to
		# filter the children.  Only Element children are returned, even if the
		# supplied XPath matches non-Element children.
		#  doc = Document.new '<a>sean<b/>elliott<c/></a>'
		#  doc.root.elements.to_a                  #-> [ <b/>, <c/> ]
		#  doc.root.elements.to_a("child::node()") #-> [ <b/>, <c/> ] 
		#  XPath.match(doc.root, "child::node()")  #-> [ sean, <b/>, elliott, <c/> ]
		def to_a( xpath=nil )
			rv = XPath.match( @element, xpath )
			return rv.find_all{|e| e.kind_of? Element} if xpath
			rv
		end

		private
		# Private helper class.  Removes quotes from quoted strings
		def literalize name
			name = name[1..-2] if name[0] == ?' or name[0] == ?"               #'
			name
		end
	end

	########################################################################
	# ATTRIBUTES                                                           #
	########################################################################

	# A class that defines the set of Attributes of an Element and provides 
	# operations for accessing elements in that set.
	class Attributes < Hash
		# Constructor
		# element:: the Element of which this is an Attribute
		def initialize element
			@element = element
		end

		# Fetches an attribute value.  If you want to get the Attribute itself,
		# use get_attribute()
		# name:: an XPath attribute name.  Namespaces are relevant here.
		# Returns:: 
		#   the String value of the matching attribute, or +nil+ if no
		#   matching attribute was found.
		# 
		#  doc = Document.new "<a foo:att='1' bar:att='2' att='3'/>"
		#  doc.root.attributes['att']         #-> '3'
		#  doc.root.attributes['bar:att']     #-> '2'
		def [](name)
			attr = get_attribute(name)
			return attr.value unless attr.nil?
			return nil
		end

		# Returns the number of attributes the owning Element contains.
		#  doc = Document "<a x='1' y='2' foo:x='3'/>"
		#  doc.root.attributes.length        #-> 3
		def length
			c = 0
			each_attribute { c+=1 }
			c
		end
		alias :size :length

		# Itterates over the attributes of an Element.  Yields actual Attribute
		# nodes, not String values.
		# 
		#  doc = Document.new '<a x="1" y="2"/>'
		#  doc.root.attributes.each_attribute {|attr|
		#    p attr.expanded_name+" => "+attr.value
		#  }
		def each_attribute # :yields: attribute
			each_value do |val|
				if val.kind_of? Attribute
					yield val
				else
					val.each_value { |atr| yield atr }
				end
			end
		end

		# Itterates over each attribute of an Element, yielding the expanded name
		# and value as a pair of Strings.
		#
		#  doc = Document.new '<a x="1" y="2"/>'
		#  doc.root.attributes.each {|name, value| p name+" => "+value }
		def each
			each_attribute do |attr|
				yield attr.expanded_name, attr.value
			end
		end

		# Fetches an attribute
		# name:: 
		#   the name by which to search for the attribute.  Can be a
		#   <tt>prefix:name</tt> namespace name.
		# Returns:: The first matching attribute, or nil if there was none.  This
		# value is an Attribute node, not the String value of the attribute.
		#  doc = Document.new '<a x:foo="1" foo="2" bar="3"/>'
		#  doc.root.attributes.get_attribute("foo").value    #-> "2"
		#  doc.root.attributes.get_attribute("x:foo").value  #-> "1"
		def get_attribute( name )
			attr = fetch( name, nil )
			if attr.nil?
				return nil if name.nil?
				# Look for prefix
				name =~ Namespace::NAMESPLIT
				prefix, n = $1, $2
				if prefix
					attr = fetch( n, nil )
					# check prefix
					if attr == nil
					elsif attr.kind_of? Attribute
						return attr if prefix == attr.prefix
					else
						attr = attr[ prefix ]
						return attr
					end
				end
				if @element.document and @element.document.doctype
					expn = @element.expanded_name
					expn = @element.document.doctype.name if expn.size == 0
					attr_val = @element.document.doctype.attribute_of(expn, name)
					return Attribute.new( name, attr_val ) if attr_val
				end
				return nil
			end
			if attr.kind_of? Hash
				attr = attr[ @element.prefix ]
			end
			return attr
		end

		# Sets an attribute, overwriting any existing attribute value by the
		# same name.  Namespace is significant.
		# name:: the name of the attribute
		# value:: 
		#   (optional) If supplied, the value of the attribute.  If
		#   nil, any existing matching attribute is deleted.
		# Returns:: 
		#   Owning element
		#  doc = Document.new "<a x:foo='1' foo='3'/>"
		#  doc.root.attributes['y:foo'] = '2'
		#  doc.root.attributes['foo'] = '4'
		#  doc.root.attributes['x:foo'] = nil
		def []=( name, value )
			if value.nil?		# Delete the named attribute
				attr = get_attribute name
				delete attr
				return
			end
			value = Attribute.new(name, value) unless value.kind_of? Attribute
			value.element = @element
			old_attr = fetch value.name, nil
			if old_attr.nil?
				store(value.name, value)
			elsif old_attr.kind_of? Hash
				old_attr[value.prefix] = value
			elsif old_attr.prefix != value.prefix
				# Check for conflicting namespaces
				raise ParseException.new( 
					"Namespace conflict in adding attribute \"#{value.name}\": "+
					"Prefix \"#{old_attr.prefix}\" = "+
					"\"#{@element.namespace(old_attr.prefix)}\" and prefix "+
					"\"#{value.prefix}\" = \"#{@element.namespace(value.prefix)}\"") if 
					value.prefix != "xmlns" and old_attr.prefix != "xmlns" and
					@element.namespace( old_attr.prefix ) == 
					@element.namespace( value.prefix )
				store value.name, { old_attr.prefix	=> old_attr,
														value.prefix		=> value }
			else
				store value.name, value
			end
			return @element
		end

		# Returns an array of Strings containing all of the prefixes declared 
		# by this set of # attributes.  The array does not include the default
		# namespace declaration, if one exists.
		#  doc = Document.new("<a xmlns='foo' xmlns:x='bar' xmlns:y='twee' "+
		#        "z='glorp' p:k='gru'/>")
		#  prefixes = doc.root.attributes.prefixes    #-> ['x', 'y']
		def prefixes
			ns = []
			each_attribute do |attribute|
				ns << attribute.name if attribute.prefix == 'xmlns'
			end
			if @element.document and @element.document.doctype
				expn = @element.expanded_name
				expn = @element.document.doctype.name if expn.size == 0
				@element.document.doctype.attributes_of(expn).each {
					|attribute|
					ns << attribute.name if attribute.prefix == 'xmlns'
				}
			end
			ns
		end

		def namespaces
			namespaces = []
			each_attribute do |attribute|
				namespaces << attribute.value if attribute.prefix == 'xmlns' or attribute.name == 'xmlns'
			end
			if @element.document and @element.document.doctype
				expn = @element.expanded_name
				expn = @element.document.doctype.name if expn.size == 0
				@element.document.doctype.attributes_of(expn).each {
					|attribute|
					namespaces << attribute.value if attribute.prefix == 'xmlns' or attribute.name == 'xmlns'
				}
			end
			namespaces
		end

		# Removes an attribute
		# attribute:: 
		#   either a String, which is the name of the attribute to remove --
		#   namespaces are significant here -- or the attribute to remove.
		# Returns:: the owning element
		#  doc = Document.new "<a y:foo='0' x:foo='1' foo='3' z:foo='4'/>"
		#  doc.root.attributes.delete 'foo'   #-> <a y:foo='0' x:foo='1' z:foo='4'/>"
		#  doc.root.attributes.delete 'x:foo' #-> <a y:foo='0' z:foo='4'/>"
		#  attr = doc.root.attributes.get_attribute('y:foo')
		#  doc.root.attributes.delete attr    #-> <a z:foo='4'/>"
		def delete( attribute )
			name = nil
			prefix = nil
			if attribute.kind_of? Attribute
				name = attribute.name
				prefix = attribute.prefix
			else
				attribute =~ Namespace::NAMESPLIT
				prefix, name = $1, $2
				prefix = '' unless prefix
			end
			old = fetch name, nil
			attr = nil
			if old.kind_of? Hash # the supplied attribute is one of many
				attr = old.delete(prefix)
				if old.size == 1
					repl = nil
					old.each_value{|v| repl = v}
					store name, repl
				end
			elsif old.nil?
				return @element
			else # the supplied attribute is a top-level one
				attr = old
				res = super(name)
			end
			@element
		end

		# Adds an attribute, overriding any existing attribute by the
		# same name.  Namespaces are significant.
		# attribute:: An Attribute
		def add( attribute )
			self[attribute.name] = attribute
		end

		alias :<< :add

		# Deletes all attributes matching a name.  Namespaces are significant.
		# name:: 
		#   A String; all attributes that match this path will be removed
		# Returns:: an Array of the Attributes that were removed
		def delete_all( name )
			rv = []
			each_attribute { |attribute| 
				rv << attribute if attribute.expanded_name == name
			}
			rv.each{ |attr| attr.remove }
			return rv
		end
	end
end