The listdirectives directive is supplied by the listdirectives plugin.

This directive generates a list of available directives.

[[!listdirectives ]]

There is one optional keyword argument, generated. Normally the listdirectives directive will list all built in directives and directives directly registered by plugins. With this keyword, listdirectives will also list directives generated later. For example, all shortcuts are directives generated in turn by the shortcut directive. They will only be listed if the generated argument is supplied.

[[!listdirectives  generated]]

This extended list is often quite long, and often contains many undocumented directives.