First of all, I'd like to say that I think there's been a serious misunderstanding here.  Placeholders were thought of, because many users who edit a wiki page (especially on Wikipedia), will see a very confusing template at the top which has nothing to do with the content of the page.  The non-technical user then gets the feeling "this is not for me" and does not even attempt to contribute to that wiki.  So, the idea of placeholders was to put something simple like {{{ <<< diagram 1 >>> }}} or {{{ <<< math formula 3 >>> }}} so that non-techies would not be scared off by scary syntax.

-- [[Chuck Smith]], 2007-Jan-25

Ok, probably the name "multiline placeholder" is unfortunate and should be replaced by "plugin" or "module". The current syntax for placeholders has two lt and gt characters, so there shouldn't be confusion.

-- [[YvesPiguet]], 2007-1-25