I am attempting to debug a php program being invoked via XMLHttp. I can't seem to do it.

It is a pretty simple situation. I have a page containing a button that runs a javascript function that uses XMLHttp to post a request to the server. Clicking the button does successfully launch the request, but I am unable to catch it in the debugger.

What should I do? Thanks.

Debugging XMLHTTP (aka AJAX) requests is no problem at all... If you have the DBGSESSID cookie set on the page that triggers the request, it should be automatically sent with the AJAX request and activate the debugger.

One solution that always works when everything else fails is to place the debugBreak() command in the php script that XMLHTTP is calling.

Okay, I renamed my test.html file to test.php and ran using F9. Debugger halts processing on line 6 which happens to be the fist <script> tag. There is no php in file. I press F9 to resume processing and the page containing the button is displayed under PhpEd output tab.

I have a breakpoint set on the first line of the php file being invoked via XMLHttp. When I click the button, PhpEd hangs. Button image remains "depressed".

I am debugging in local Apache server configured as a 3rd party Web server in PhpEd.

Certainly, a pure HTML/Jscript file has no php but being processed by php, it is converted to series of echos and that's why debugger allows to step through it.

You may want to add DBGSESSID to the URL you call with XMLHttp, or put DebugBreak in the code called by this URL.
For example with DBGSESSID your URL might look like this:

http://localhost/adirectory/ascript.php?DBGSESSID=1

or your code might look like this:
<?php
DebugBreak();
// the rest of the script is below
...
?>