Because they can't do that. XML is just the output, it's not a programming language. You need PHP to output the XML.
It's not my opinion. It's how it's done. I am in this field for four years now, so I know how this works.
It doesn't reduce that need for heavy apps, because that's not what AJAX does.
AJAX does only the following:
Send user input to the server and display the output of that action without having to refresh the page. Nothing else! It does not act on the server, it doesn't access the database, nothing! It completely sits on the user's pc and gives the user a streamlined web interface. That's what I am trying to tell you for countless posts now.
I quote myself:
So please' date=' read that article yourself first.
If you don't understand the technology, please learn it first before telling me I'm wrong.
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