Parser function extensions

A "parser function" is a template-like construct which returns a value based on at least one unnamed parameter, separated from the function name by a colon ":"; there may be more parameters which, like those of ordinary templates, each preceded by "|". In the case of a hash character (#) at the start of the function name (which prevents collision with namespaces and interwiki prefixes) this may or may not be considered part of the name. If it is considered part of the name, the syntax is of the form



Arguments cannot directly contain "|" or "}}" except as part of the code of a template call, parser function call, variable, link or image, but they can contain them arbitrarily using a template, e.g., or a parser function.

The code can specify whether the function name is case-sensitive.

The separation of the arguments from each other is with "|", and from the function name is with the first ":" The expansion of each of these pieces is standard as in Special:ExpandTemplates (which is a good place to experiment by the way if you are learning this stuff) and is beyond the control of the parser function.

However, everything else can be different for each parser function, including:
 * whether an argument is just a value, or of the form parname = parvalue, or whatever
 * if applicable, whether parameter names are case-sensitive

Syntax prescribed by a parser function extension
In view of the above, it is advantageous to make an extension such that the syntax to be used in an argument does not contain the pipe character "|" or double braces (more specifically, double closing braces "}}" ). This in spite of the fact that a pipe character would otherwise seem a suitable symbol for e.g. a choice or union (see e.g. ). Allowing such codes is harmless, if also an alternative code is allowed, e.g. "\" for "|".