Preprocessor directives are similar to a [[WikiLink]] in form, except they
contain spaces and parameters. The general form is:

\\[[directive param="value" param="value"]]

This gets expanded before the rest of the page is processed, and can be used
to transform the page in various ways.

Note that if a preprocessor directive has no parameters, a space still must
be put after its name, to avoid confusion with a [[WikiLink]]. For example:

\\[[pagecount ]]