> I donā€™t think it is as much a matter of stealing as that they just had 
> to pick a delimiter character - had they used e.g. % instead of ?, the 
> ASP and JSP folks would perhaps not have liked that.

I don't know the early history of PHP, but I strongly suspect that they
use ? for the same reason that XML uses it, namely it is the proper
way of forming an SGML processing instruction.  The name after
the ? tells you what processor is supposed to handle that instruction,
so there is no conflict between XML and PHP if you use properly
formed processing instructions.

For some reason, PHP also chose to allow an abbreviated form, that
doesn't indicate the processor, so will cause conflicts, but that
was just a convenience for pure HTML use.  It makes the resulting
input document invalid, whereas the full form is valid SGML.