Themes

Some requirements:

Install and uninstall should be easy and non-destructive
- No unrecoverable data should be lost or overwritten
- Should be symmetrical: everything returns to its original state after installing and then uninstalling a theme (assuming no other changes)

Previewing themes should be easy
- Should be able to install several themes, apply them one by one, revert to the original appearance, and uninstall those themes
- Switching from one theme to another should be a one-step operation. I shouldn't have to install a theme and then manually change the page template and CSS settings on 53 different sections. Likewise when reverting back to the original appearance.
- Ideally there should be a way to preview a theme without affecting a live site. Either by creating a test section, and applying a theme to that section only (i.e. a per-section theme setting), or by allowing logged-in admin users to switch themes on the fly when viewing public pages.

Names should be relative
- Say I have two sections, "article" and "gallery", set to use the "default" and "gallery" page templates respectively. If I switch to a different theme, those sections should automatically use the "default" and "gallery" templates from the new theme, assuming they exist. Same deal when switching back. And likewise for error pages.
- Things like POST urls for the search form, image URLs in page templates and in CSS stylesheets, navigation links etc should all be relative, so they work regardless of whether a site is installed in the root or in a subdirectory; also regardless of whether the theme is applied to the entire site or to a single section (assuming we allow per-section themes). Remember that work has already begun on nested sections.
- Theme Support should be coupled with a possible [Naming Convention] that conforms to the mechanism's requirements and eases maintenance.