Source

File: wp-includes/rss.php

function feed_cdata ($p, $text) {

		if ($this->feed_type == ATOM and $this->incontent)
		{
			$this->append_content( $text );
		}
		else {
			$current_el = join('_', array_reverse($this->stack));
			$this->append($current_el, $text);
		}
	}