Source

File: wp-includes/rss.php

function feed_start_element($p, $element, &$attrs) {
		$el = $element = strtolower($element);
		$attrs = array_change_key_case($attrs, CASE_LOWER);

		// check for a namespace, and split if found
		$ns	= false;
		if ( strpos( $element, ':' ) ) {
			list($ns, $el) = explode( ':', $element, 2);
		}
		if ( $ns and $ns != 'rdf' ) {
			$this->current_namespace = $ns;
		}

		# if feed type isn't set, then this is first element of feed
		# identify feed from root element
		#
		if (!isset($this->feed_type) ) {
			if ( $el == 'rdf' ) {
				$this->feed_type = RSS;
				$this->feed_version = '1.0';
			}
			elseif ( $el == 'rss' ) {
				$this->feed_type = RSS;
				$this->feed_version = $attrs['version'];
			}
			elseif ( $el == 'feed' ) {
				$this->feed_type = ATOM;
				$this->feed_version = $attrs['version'];
				$this->inchannel = true;
			}
			return;
		}

		if ( $el == 'channel' )
		{
			$this->inchannel = true;
		}
		elseif ($el == 'item' or $el == 'entry' )
		{
			$this->initem = true;
			if ( isset($attrs['rdf:about']) ) {
				$this->current_item['about'] = $attrs['rdf:about'];
			}
		}

		// if we're in the default namespace of an RSS feed,
		//  record textinput or image fields
		elseif (
			$this->feed_type == RSS and
			$this->current_namespace == '' and
			$el == 'textinput' )
		{
			$this->intextinput = true;
		}

		elseif (
			$this->feed_type == RSS and
			$this->current_namespace == '' and
			$el == 'image' )
		{
			$this->inimage = true;
		}

		# handle atom content constructs
		elseif ( $this->feed_type == ATOM and in_array($el, $this->_CONTENT_CONSTRUCTS) )
		{
			// avoid clashing w/ RSS mod_content
			if ($el == 'content' ) {
				$el = 'atom_content';
			}

			$this->incontent = $el;

		}

		// if inside an Atom content construct (e.g. content or summary) field treat tags as text
		elseif ($this->feed_type == ATOM and $this->incontent )
		{
			// if tags are inlined, then flatten
			$attrs_str = join(' ',
					array_map(array('MagpieRSS', 'map_attrs'),
					array_keys($attrs),
					array_values($attrs) ) );

			$this->append_content( "<$element $attrs_str>"  );

			array_unshift( $this->stack, $el );
		}

		// Atom support many links per containging element.
		// Magpie treats link elements of type rel='alternate'
		// as being equivalent to RSS's simple link element.
		//
		elseif ($this->feed_type == ATOM and $el == 'link' )
		{
			if ( isset($attrs['rel']) and $attrs['rel'] == 'alternate' )
			{
				$link_el = 'link';
			}
			else {
				$link_el = 'link_' . $attrs['rel'];
			}

			$this->append($link_el, $attrs['href']);
		}
		// set stack[0] to current element
		else {
			array_unshift($this->stack, $el);
		}
	}