code: function() {
  		var contentItem,
  			isClosable,
  			len,
  			i;
  
  		isClosable = this.header._isClosable();
  
  		for( i = 0, len = this.contentItems.length; i < len; i++ ) {
  			if( !isClosable ) {
  				break;
  			}
  
  			isClosable = this.contentItems[ i ].config.isClosable;
  		}
  
  		this.header._$setClosable( isClosable );
  	}
docs: Validates that the stack is still closable or not. If a stack is able
  to close, but has a non closable component added to it, the stack is no
  longer closable until all components are closable.
  
  @returns {void}