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.
Usage
{{When on basepage |result if on a basepage (|result if on a subpage) (|result if on a subsubpage) (|page=pagename)}}
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").
Handling equals-signs ("=")
Use numbered parameters if their values include equals-signs ("="), i.e.
- {{When on basepage |1=basepage result (|2=subpage result) (|3=subsubpage result)}}
page parameter
The page parameter is included for testing/demonstration. For example:
- {{When on basepage |(basepage result)|(subpage result)|page=User:Example/test}}
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. Template:Tld) is used.
page also accepts variables, e.g. {{When on basepage|(basepage result)|(subpage result)|page={{{page|}}} }}
Technical note
This template detects subpages in all namespaces, including those without the MediaWiki subpage feature enabled.
Alternatives for simpler text
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:
- {{#ifeq: {{#titleparts:{{PAGENAME}}|1|1}} | {{PAGENAME}}
- | {{documentation}}
- | {{template sandbox notice}}
- }}
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.
See also
{{Ns has subpages}}