code: function elementBoundaryEval( checkStart ) {
  		var whitespaces = CKEDITOR.dom.walker.whitespaces(),
  			bookmark = CKEDITOR.dom.walker.bookmark( 1 );
  
  		return function( node ) {
  			// First skip empty nodes.
  			if ( bookmark( node ) || whitespaces( node ) )
  				return true;
  
  			// Tolerant bogus br when checking at the end of block.
  			// Reject any text node unless it's being bookmark
  			// OR it's spaces.
  			// Reject any element unless it's being invisible empty. (#3883)
  			return !checkStart && isBogus( node ) ||
  				node.type == CKEDITOR.NODE_ELEMENT &&
  				node.is( CKEDITOR.dtd.$removeEmpty );
  		};
  	}
docs: Evaluator for CKEDITOR.dom.element::checkBoundaryOfElement, reject any text node and non-empty elements unless it's being bookmark text.