Template:When on page/doc

This is the When on page meta-template.

It helps other templates detect what page they are on. It uses pattern matching on the pagename. It can reuse the same input on multiple matching patterns.

This template is an extended version of When pagename is.

Usage
This template takes two or more parameters. The data to return when a match is found is fed as numbered parameters. Most of the other parameters don't have fixed names, instead they are part of the pattern matching. Like this:

If the template is on "Template:Example/doc" the code above will return this:

If the template is on any other page than a /doc or /sandbox page it will return this:

Here is a description of the full pattern matching:

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. The numbered parameters don't need to be contiguous, you could just as well use 3, 5, 120 and so on.

There's no limit to the number of parameters (patterns or numbered) that you can use, other than what the servers and MediaWiki system can handle.

Most of the matching is case-sensitive. For instance " " matches "User:Example/test" but not "User:Example/Test".

Matching on partial subpage names such as " " 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:

The code above will render nothing when on a /doc page. But when on a /sandbox page it will return this:

And when on any other page it will return this:

Partial subpage names
This template can also match on partial subpage names. Like this:

If on "User:Example/Archive 5" the code above will return this:

The parameter name " " 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 " ", " " and " " works, but using " " or " " doesn't work.

Longer patterns match first, thus if both " " and " " are defined, and the current page is "User:Example/Something", then the data from " " will be used.

"page" parameter
For testing and demonstration purposes this template can take a parameter named page. Like this:

No matter on what kind of page the code above is used it will return this:

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:

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 When on template page. Like this:

If on "User:Example/doc" the code above will return nothing. But if on "Template:Example/doc" it will return this:

Technical details
This template detects subpages even when used in namespaces that doesn't have the MediaWiki subpage feature enabled. Thus this template works the same in all namespaces.

For more technical details, see the talk page.