W3C-validator does not validate all of a given XHTML page with PHP code

Hello and to whomever it may concern
 
I have been using the W3C Validator a lot and find it a great tool to
assist me in the creation of well-formed code. Especially since I'd
rather be photographing than writing code for the browsers.
Recently I have created a page with a tool to calculate specific values
for panoramas to be displayed by means of Java. Input values in XHTML ->
calculated by PHP -> output values in XHTML - all on one page (1,2). 
To me all works fine as anticipated and seemingly passes the validator
with success.
But I am certain that not all XHTML code really gets crunched by the
validator as the page does contain some 'ill-formed' XHTML code.
So what is it that fools the validator? In the first place this is due
to the code-writer and I positive it must be some PHP code stopping the
validator. Why? Well, because when I run the calculator on that page and
save the browsers 'sourcecode' in an XHTML file and then run that code
(3) through the validator the result is quite different. Actually it
does not pass, as mentioned.
You may try for yourself, here are the urls to that page I am referring
to in this post.
http://www.halo-photographs.com/pano-calc/panorama-calculator.php (1)
or
http://www.halo-photographs.com/pano-calc/panorama-calculator.html (2)
(both are equal and validate positive).
 
The same page but drawn from the Browser's source and then saved (does
not validate, because it contains obvious ill-formedness.
http://www.halo-photographs.com/check/panorama-calculator-source.html
(3)
 
Hence (at least in this case) the W3C-validator does not validate all of
a given page that contains PHP -q.e.d..
 
Thought this might be of interest to the creators of the W3C-Validator.
Looking forward to receiving highly appreciated feedback and adivce.
 
Best wishes, Hans.
 
PS: By the way, thanks a lot for providing this great validation
service.
___________________________________
Hans Loepfe
Alte Landstrasse 99
CH - 8803 Rüschlikon
Schweiz / Suisse / Svizzera / Switzerland
 
Mobile: 079 764 4422
www.HALO-Photographs.com <http://www.halo-photographs.com/> 
___________________________________