This is the ((When on basepage)) meta-template. It helps other templates detect if they are on a basepage (i.e. a page whose name matches the pattern "x:x") subpage ("x:x/x") or subsubpage ("x:x/x/x").
An alternative way to detect whether a page is a subpage is to combine the parser functions #ifeq:
and #titleparts
. See Alternatives for simpler text below.
For example, ((When on basepage|Basepage|Subpage)) on the page "User:Example" would return: Basepage
whilst on "User:Example/page" (or "User:Example/page/page", "User:Example/page/page/page", etc.) it would return: Subpage
On a subsubpage such as "User:Example/page/page" (or "User:Example/page/page/page", etc.), ((When on basepage|Basepage|Subpage|Subsubpage)) would return: Subsubpage
Use an empty parameter to specify no action for a particular type of page. ((When on basepage|Basepage||Subsubpage)) on "User:Example/page", for example, would return nothing, but would return "Subsubpage" if on "User:Example/page/page", "User:Example/page/page/page", etc. (and "Basepage" if on "User:Example").
Use numbered parameters if their values include equals-signs ("="), i.e.
The page parameter is included for testing/demonstration. For example:
Regardless of where the above is placed, it will return: (subpage result)
(because "User:Example/test" is a subpage). The page doesn't have to exist.
If page is left empty (|page=
) or undefined, the page where the template is transcluded (i.e. ((PAGENAME))
) is used.
page also accepts variables, e.g. ((When on basepage|(basepage result)|(subpage result)|page=(({page|))} ))
This template detects subpages in all namespaces, including those without the MediaWiki subpage feature enabled.
A subpage can be detected without using another template, by instead using the title-splitting parser function #titleparts
with #ifeq
:
((#ifeq:((#titleparts:((PAGENAME))|1|1))|((PAGENAME)) | [...code if on a basepage...] | [...code if on a subpage...] ))
For example, many templates can check if the page is a /sandbox version, by the similar markup with #ifeq
and #titleparts
:
That simple logic works because Template:Template sandbox notice also checks the page name for "/sandbox" before displaying the sandbox notice; otherwise, any other subpage would show no extra text. By avoiding a template, and using a single #ifeq
, then the processing uses only +2 expansion depth levels, rather than +7 levels, and avoids "wp:exceeded template limits" inside a complex /doc page.