It is good practice to use relative links for a variety of reasons, however, within RSS feeds this can cause problems, as the links are often interpreted as relative to the page where the RSS is viewed, not relative to the source page. For example, this link works fine when viewed on my site, it links to the 'top level' page, but might break when in an aggregator. I'm not really happy to go back and change relative links to absolute links, this seems like a lot of hassle - and I don't really want to use absolute links in the future. Therefore, a plugin for movabletype seems ideal - unfortunately I don't have the perl skills to do it!
There is a plugin which takes absolute URLs generated by MT and makes them relative. I'm looking to do the reverse for relative URLS within posts that I need to make absolute for RSS purposes.
It'd be called 'Relative2Absolute' and would be a text processing option (a bit like the Amputator plugin) which monitors for relative links, and when detected, subsitutes a base URL in front of them. As a first pass it could match anything which is a href=" but not a href="http://
This would then let the RSS feeds be filtered to use absolute links, but leave the relative links within posts untouched.