Hi elpnt11583,
Thanks for your question!
Currently QuarkXPress does not have app development language support (like PHP, ASP, ColdFusion, etc.)... and you cannot view/edit the code within the XPress layout. You can edit the HTML that XPress exports (its all standards compliant HTML), but it would likely take you longer to modify the HTML than it would to write an entirely new page by hand.
You can use the forms tools in XPress to submit actions via the HTTP Get and Post methods to specific URLs (so if you are submitting form data to a CGI, PHP, ASP, etc. script). I would imagine if your client is requiring PHP, they likely have more complex requirements for integration with back end systems than QuarkXPress can support (e.g. datasource driven dynamic content, login/session management, etc.).
We are looking into the feasibility of possibly supporting development languages in the web layout and 2 way, dynamic datasource connectivity, but I couldn't tell you what future version that might be.
Hope that helps!
-Drew