Template:P1/Doc/PN

Pn
The templates , where " " is a number, each return the corresponding.

They are typically used in other templates when there are several values that can be returned, one of which is the named parameter. Whether to use is calculated.

E.g.

returns parameter 1 if it's non blank, otherwise parameter 2.

This usage might be chosen because the following more straight forward implementation would have the undesired side effect of stripping whitespace from the beginning and end of parameters 1 and 2 (a side effect of #if:).