This is the {{When pagename is}} meta-template. It helps other templates detect what page they are on, using pattern matching on the pagename.
Usage
This template takes one or more parameters. Most of the parameters don't have fixed names, instead they are part of the pattern matching. Like this:
{{When pagename is
| /doc = Doc page text
| other = Other pages text
}}If the template is on "Template:Example/doc" the code above will return this:
- Doc page text
If the template is on any other page than a /doc page it will return this:
- Other pages text
Here is a description of the full pattern matching:
{{When pagename is
<!-- Match on full pagename -->
| User:Example/test = Text for "User:Example/test".
| User:Example = Text for "User:Example".
| User talk:Example = Text for "User talk:Example".
<!-- Match on full basepage name, when on a basepage or its subpages -->
| User:Example/+ = Matches "User:Example" and "User:Example/test".
<!-- Match on pagename, when on a basepage -->
| Example = Matches "User:Example", "User talk:Example", "Template:Example"
and so on, but not "User:Example/something".
<!-- Match on full basepage name, when on a subpage -->
| User:Example/* = Matches "User:Example/something", but not "User:Example".
| User talk:Example/* = Matches "User talk:Example/something".
<!-- Match on basepage name, when on a subpage -->
| Example/* = Matches "User:Example/something" and "User talk:Example/something".
<!-- Match on subpage name -->
| /something = Any pagename that ends in "/something".
| /doc = Any pagename that ends in "/doc".
<!-- Match on partial subpage name (case-insensitive) -->
| /some* = Any subpage name beginning with "/some" or "/Some".
| /arch* = Matches "User talk:Example/Archive 1".
<!-- Defaults -->
| basepage = Text for any basepage.
| subpage = Text for any subpage.
| other = Text for any page.
}}The matching goes from top to bottom, and returns the first parameter that matches. "Top to bottom" means the order shown above, not the order you happen to feed the parameters.
There's no limit to the number of parameters that you can use, other than what the servers and MediaWiki system can handle.
Most of the matching is case-sensitive. For instance "/test" matches "User:Example/test" but not "User:Example/Test".
Matching on partial subpage names such as "/some*" has some limitations, see its own section below.
If an empty (but defined) parameter matches, the matching stops and the template returns an empty string. That's on purpose and can be used like this:
{{When pagename is
| /doc =
| /sandbox = Sandbox text
| other = Other pages text
}}The code above will render nothing when on a /doc page. But when on a /sandbox page it will return this:
- Sandbox text
And when on any other page it will return this:
- Other pages text
Partial subpage names
This template can also match on partial subpage names. Like this:
{{When pagename is
| /archiv* = Archive page text
| other = Other pages text
}}If on "User:Example/Archive 1" the code above will return this:
- Archive page text
The parameter name "/some*" must be lower case. But it matches subpage names in both upper and lower case such as "User:Example/SomeThing" and "User:Example/something".
The partial matching only supports matching on 4, 6 and 8 characters. Thus using "/some*", "/someth*" and "/somethin*" works, but using "/som*" or "/somet*" doesn't work.
Longer patterns match first, thus if both "/somethin*" and "/some*" are defined, and the current page is "User:Example/Something", then the data from "/somethin*" will be used.
"page" parameter
For testing and demonstration purposes this template can take a parameter named page. Like this:
{{When pagename is
| /test = Test pages text
| other = Other pages text
| page = Template:Example/test
}}No matter on what kind of page the code above is used it will return this:
- Test pages text
The page parameter makes this template behave exactly as if on that page. The pagename doesn't have to be an existing page.
If the page parameter is empty or undefined, the name of the current page determines the result.
You can make it so your template also understands the page parameter. That means you can demonstrate the different appearances of your template in the documentation for your template. Then do like this:
{{When pagename is
| /test = Test pages text
| other = Other pages text
| page = {{{page|}}}
}}Namespace matching
This template doesn't have namespace matching. If you need that then combine this template with one of the namespace-detection templates such as {{Template:Template other}}. Like this:
{{When on template page
| {{When pagename is
| /doc = Template doc page text.
}}
| <!--(action if not on a Template: page)-->
}}If on "User:Example/doc" the code above will return nothing. But if on "Template:Example/doc" it will return this:
- Template doc page text.
Technical details
This template detects subpages even when used in namespaces that don't have the MediaWiki subpage feature enabled. Thus this template works the same in all namespaces.
For more technical details, see the talk page.