Extension:Page Forms/Page Forms and templates

Page Forms is, at its heart, a system for editing template calls within wiki pages. (Though it can also edit page sections.) See Help:Templates for a full explanation of templates within MediaWiki.

Why does Page Forms support editing templates and page sections, but not, say, free-form category tags within pages? That's because the philosophy of Page Forms is that all true data in MediaWiki - including data, category information and anything else - should be stored within templates. That's for several reasons:
 * templates provide a clear guideline for what information belongs in which pages, avoiding ambiguity about the data structure
 * templates hide the complex syntax involved in displaying and storing information, making editing easier
 * templates allow for easier changes to the structure and display, since a change across a large group of pages can potentially be done just in one place, instead of requiring edits to all of them.

Multiple values for the same field
Page Forms makes one main contribution to the operating of templates: it defines the parser functions  and , which provide support for having multiple values for a single field, delimited by a comma or other character. These parser functions "map" some text processing onto each value. This can be as simple as turning each value into a link, although there can be more complex processing, like turning each value into a category tag, an image tag, a Semantic MediaWiki property tag, and so on.

and  can also be used outside of a template context. In fact, the ideal place for these functions to be defined might be in the ParserFunctions extension, or even in core MediaWiki itself. At the moment, however, there is no plan to move these functions.

arraymap
The generic call for this function is:

The function splits the 'value' by the 'delimiter', and then, for each one, applies the same mapping that 'formula' does to 'variable', and finally joins all the values again using the 'new_delimiter'. For example, if you have a form that populates the field 'author', and you want the values for that field to be separated by commas and to each get the semantic property 'Has author', you could add the following to the template code, in place of a regular semantic tag:

Essentially this function 'maps' the property tag onto each comma-delimited value in the field. (The 'delimiter' parameter defaults to "," and 'new_delimiter' defaults to ", " (note the extra space) if they are not set.) The user can thus enter all the values on the same line, with or without spaces around the commas. (Note, by the way, that the "x" is used here as an internal variable: if the property name itself contains the letter "x", that will lead to problems, and you should replace the letter "x" with some character or string that does not appear in the property name, like " ".)

The 'new_delimiter' parameter is especially helpful if none of the resulting values are actually displayed, because by default such a thing would show up as a string of commas. A common example of that is if the original value holds a list of category names, and each name gets turned into a category tag, but is not actually displayed.

To avoid displaying commas in that case, you should set the 'new_delimiter' value equal to a space. Using just "| " at the end won't work, because the MediaWiki parser will ignore it - instead, the easiest approach is to use "\s", which gets translated into a space Here is how such a thing could be called:

If you use the 'CreateTemplate' or 'CreateClass' pages to create a template, and you specify that a field that can take more than one value, then an  call will be automatically added to the generated template.

arraymaptemplate
There are some kinds of mapping that are complex enough that they cannot be placed in the  function. For this purpose, you can instead use the similar  function.

To use this function, first create a template that takes in a single field (it should be referred to in the template as ) and applies the mapping you would like to that field. Then apply  onto the main template field just as you would with , using the following format:

...where 'template' is the name of the mapping template in question.

For example: to display a (comma-separated) list of authors as a numbered list, you could first create a template called "Numbered author", with the following contents:

...then call the following:

Using \s and \n in the delimiter
For both  and , the string " " in the value of either 'delimiter' or 'new_delimiter' will get converted into a space, while the string " " in either parameter will get converted into a newline.

It should be noted that, if you want an actual line break to appear between values, you should have two newlines (i.e, " ") as the delimiter, since MediaWiki requires two newlines in order to display a line break.

Template-based special pages
Page Forms defines three special pages that relate to templates:
 * Special:Templates, which lists all the templates in the wiki,
 * Special:CreateTemplate, and
 * Special:CreateClass.

Both of the latter two pages (i.e., Special:CreateTemplate and Special:CreateClass) can be used to generate templates automatically.

As with the  and   functions, there is a case to be made that Special:Templates and Special:CreateTemplate really should be defined somewhere other than in Page Forms. However, again there is no current plan to move them.