‘Play All’ Functionality
 First, set a register value for the button when it is pressed.  Then, have a statement at
 each post command that if that particular register is set, goto the next title. Otherwise,
 goto the menu. 

 Below is a simple demonstration.
 Button1 (the 'play all' button) sets the register (in this case, g4) to 1, so everytime
 the post command is excuted, if it is '1', then goto the next title. If the second button
 is pressed, it simply plays that one particular title.

 <?xml version="1.0" encoding="UTF-8"?>
 <dvdauthor dest="C:\test">
  <vmgm>
  </vmgm>
  <titleset>
    <menus>
      <pgc>
        <button>g4=1; jump title 1 chapter  1; </button>
        <button>g4=0; jump title 1 chapter  1; </button>
       <vob file="C:\test\menusub1.mpg" pause="5"/>
      </pgc>
    </menus>
      <titles>
       <video format="ntsc" />
        <pgc>
          <vob file="C:\test\title1.mpg" chapters="00:00:00.00" />
          <post>if (g4==1) jump title 2; call menu;</post>
        </pgc>
        <pgc>
          <vob file="C:\test\title2.mpg" chapters="00:00:00.00" />
          <post>if (g4==1) jump title 3; call menu;</post>
        </pgc>
        <pgc>
          <vob file="C:\test\title3.mpg" chapters="00:00:00.00" />
          <post>call menu;</post>
        </pgc>
      </titles>
  </titleset>
 </dvdauthor>