General transformation tags / snippets ?

Do they exist or are they possible/practical in MODx ?

In my static-XML homepage "offline engine" i just write a thing like "<lj user="name" msg="id" /> and XSL styleseet automagicaly converts it to the link "http://livejournal.com/users/name/id". If later on i’ll decide to generate extra links for user info, or even Google search of all his messages - i’ll change one XSL and this will affect all such tags. (I think it’s quite easy to do, but cumbersome - an SQL request for snippet at every tag, what if hundred of them on a page ?)

Also, how can i do the following:
[SpecialFormatSnippet ? param=val]
..... some data formatted for that snippet, maybe CSV ....
.... and some more
[EndOfSpecialFormatSnippet]

And finally, the hardest thing:
Input: <p><h3>Header</h3>Text text text</a>
Output: Fancy table with graphics, like at http://dpreview.com
Can it be done easily ? In my knee-made XML+XSL i can )

Right now, we’re not using XML/XSLT. I suppose a module could be made to allow the use of it, however, that will be most effectively done in the highly modular rewrite that’s going on now (all off the same DB, btw). Stay tuned... !