Just thought I'd add my 2c....
While XML was not created by Microsoft (it is an initiative of the W3c and luciddream stated) - Microsoft is one of the largest supporters of the standard (I understand .NET and XP products make heavy use of it)
XHTML applys XMLs structure rules to the HTML standard - things like "No empty tags, all tags should be closed"
For example, in HTML you define an image thus:
<img src="image.gif" ...>
XHTML requires all tags should be closed, so you would then do:
<img src="image.gif" ...></img>
But XHTML also requires that there be no empty tags, so you would then change it to:
<img src="image.gif" ... />
Another rule is that structure in opening/closing tags must be strictly followed, eg the following tag structure would not validate as XHTML:
<font...><i></font></i>
But the following will:
<font...><i></i></font>
Anyway, I'm rambling on. The point I was intending to make was that XHTML is geared towards a common standard in the way Markup is coded - keeping everything structured and logical - no spagetti code
