Board Thread:Support Requests - Getting Technical/@comment-26891040-20140612181032/@comment-2170536-20140612234331

In the interest of completeness, spaces are perfectly acceptable when using the internal link format (e.g.  ,  This is a page name with spaces ). The only time spaces can't be used is when the link uses the external format, e.g.   (which of course doesn't actually display the image at all), because everything that comes after the first space is assumed to be the link's display text. This isn't a problem for the internal format because the display text is delimited by a pipe character.

MissingNo. is absolutely correct regarding the "File:" prefix being required, but replacing the spaces with underscores is not strictly necessary. It does work either way, though, so if you prefer to add your internal links with underscores, they work just as well.