I dont want to let dragger pass the line

programming flash
1

I was just working on the tutorial named Slider Bars. And I wanted to add to buttons to it (Volume Up Button and Volume Down Button). To let the user make the volume up or down with the buttons. And the interface was like the attached picture named picture1.

I put this code to volume up

 
on (release) {
 dragger._x +=5;
}

And this one to volume down

 
on (release) {
 dragger._x -=5;
}

And when I test the movie I have faced the truth (Attached picture2 ).
How can I solve this guys please help.I have attached my fla file to. So any help will be great.