PmWiki has the capability of classifying pages into groups of related pages. By default page links are between pages of the same group; to create a link to a page in another group, add the name of the other group and a dot or slash to the page name. For example, links to Main.HomePage could be written as:
*[[Main.HomePage]] *[[Main/HomePage]] *[[Main(.HomePage)]] *[[Main.HomePage | link text]]
Creating a new group is as easy as creating new pages; simply edit an existing page to include a link to a page in the new group, then click on the '?' to edit the page. By default, group names must start with a letter (but this can be changed by the wiki administrator).
For example, to make a page called Bar in the group Foo, create a link to [[Foo/Bar]] and follow the link to edit that page.
To list all the groups in a site, try the markup
Each group can also have GroupHeader or GroupFooter pages that contain text to be automatically prepended or appended to every page in the group. A group can also have a GroupAttributes page that defines attributes (read and edit passwords) shared by all pages within the group.
Each page can also have its own individual read/edit password that overrides the group passwords (see Passwords).
Any page that has the same name as its group is considered to be the default "start page" for that group; if such a page does not exist then HomePage is used as the start page for the group instead.
No, PmWiki does not have subpages. Pm's reasons for not having subgroups are described at PmWiki:HierarchicalGroups, but it comes down to not having a good page linking syntax. If you create a link or pagename like
[[A.B.C]] PmWiki doesn't think of "B.C" as being in group "A", it instead thinks of "C" as being in group "AB", which is a separate group from "A". Wiki administrators can look at Cookbook:SubpageMarkup and Cookbook:IncludeWithEdit for recipes that may be of some help with developing subgroups or subpages.