-It's also possible to write a WikiLink that uses something other than the
-page name as the link text. For example `\[[foo_bar|SandBox]]` links to the
-SandBox page, but the link will appear like this: [[foo_bar|SandBox]]
+It's also possible to write a WikiLink that uses something other than the page
+name as the link text. For example `\[[foo_bar|SandBox]]` links to the SandBox
+page, but the link will appear like this: [[foo_bar|SandBox]]. The reason you
+**have to use underscores in place of spaces in WikiLinks** is so that
+`ikiwiki` can distinguish your WikiLink from a PreProcessorDirective.
+
+(Note: previously, you could actually use spaces if you specify the target
+link following the pipe symbol (`|`), as in the above, but this has been
+disabled shortly after version 2.8).