Edge Animate CC :: How To Play Reverse Between Label A And B

I have a symbol，some timaline and labels in it.so now I want to play reverse between the Label A and Lable B but the action syntax is like

test1_play.playReverse();
 
so how can I play reverse rom LableB to LableA? 
 
sym.playReverse ( position, executeTriggers )

position defaults to the current playhead position (which defaults to 0); If play is issued and the playhead is at the end of the timeline, play from the end.executeTriggers can be true, false, or null and indicates whether triggers at the starting position are fired:true - all triggers at the starting position are fired.false - no triggers are fired at the start point.null, undefined or omitted - triggers are fired at the starting position only if the timeline is being played for the first time, or if the starting position is different than the current playhead position as returned by getPosition().Description: Play the default timeline in reverse from the given position given in milliseconds (if position is a number) or as a label (if position is a string).