Simple mark-up for CMS

[gsoper]

I'm designing/coding a content management system in PHP and am currently considering how the users will add textual content. I would like them to be able to use some kind of simple mark-up, like a very limited subset of HTML, probably with a more friendly naming scheme. Does anybody have experience of such a thing? I'm thinking an XML application is the proper answer but when I consider the DTD and parser it seems like an overkill solution if I'm starting from scratch.
Does anybody have any advice or suggestions on this? I'm sure it's been done before but I don't know where to look, is there something existing I can use or adapt? Has anybody tried this kind of thing before?

I'd really appreciate any kind of help in this,
Geoff

[me']

It's not XML-based, but it's the sort of thing you want: Textile Style Markup.