code: function addSafely( collection, element, database ) {
  		// 1. IE doesn't support customData on text nodes;
  		// 2. Text nodes never get chance to appear twice;
  		if ( !element.is || !element.getCustomData( 'block_processed' ) ) {
  			element.is && CKEDITOR.dom.element.setMarker( database, element, 'block_processed', true );
  			collection.push( element );
  		}
  	}
docs: Add to collection with DUP examination. @param {Object} collection @param {Object} element @param {Object} database