What characters are allowed in Page and Space names?

All characters are supported in both Page and Space names (except if you're using a very old XWiki versions, prior to XWiki 4.x).

Note that if you wish to link to a page with some special characters in its Page/Space name and you're using the XWiki Syntax 2.0+, you'll need to escape those characters (see the model reference documentation. Here's an example with a : in the Space name and a . in the Page name: