Demo for Help:Link in a Meta namespace where subpages are not supported
{{FULLPAGENAME}} gives Help:Link/a/b.
{{PAGENAME}} gives Link/a/b.
{{SUBPAGENAME}} gives b.
{{BASEPAGENAME}} gives Link/a.
[[../]] fails: Help:Link/a.
[[../a]] fails: Help:Link/a/a.
[[../b]] fails: Help:Link/a/b.
[[/b]] fails: /b isn't below this page.
{{fullurl:{{NAMESPACE}}:{{BASEPAGENAME}}/b}} gives http://www.lensovet.net/~sysadmin/w/Help:Link/a/b.
http://www.lensovet.net/~sysadmin/w/Help:Link/a/b/../c
See also Special:Prefixindex/Help:Link/ and Link/a.