code: function() {
  			if ( this.locked ) {
  				// Decrease level of lock and check if equals 0, what means that undoM is completely unlocked.
  				if ( !--this.locked.level ) {
  					var update = this.locked.update;
  
  					this.locked = null;
  
  					// forceUpdate was passed to lock().
  					if ( update === true )
  						this.update();
  					// update is instance of Image.
  					else if ( update ) {
  						var newImage = new Image( this.editor, true );
  
  						if ( !update.equalsContent( newImage ) )
  							this.update();
  					}
  				}
  			}
  		}
docs: Unlocks the snapshot stack and checks to amend the last snapshot.
  
  See {@link #lock} for more details.
  
  @since 4.0