function onNode( node, index, parent ) {
	var className;
	if ( parent && parent.tagName === 'pre' && node.tagName === 'code' ) {
		debug( 'Found a `code` element...' );
		className = node.properties.className || [];

		// `text` is not a registered highlight.js language, so we need to disable attempted highlighting...
		if ( indexOf( className, 'language-text' ) !== -1 ) {
			debug( 'Found a `code` element labeled as text. Adding a `no-highlight` class...' );
			className.unshift( 'no-highlight' );
		}
	}
}
Callback invoked upon visiting a tree node.

@private
@param {Object} node - AST node
@param {number} index - position of node in parent
@param {Object} parent - parent AST node