It incorporates features into your RSS feed that normally either aren't there or need to be added by hand. Things like the categories, post author, comment link, and copyright information if you choose.
You can! WP functions done work very well in freetext, but there's no reason to have most of them in your feed anyway. PHP works just fine though.
I've thought about it, but I'm open to suggestions on what to add. Get in contact with me and we'll talk about it over a cup of coffee.
Sociable added this function into it's own plugin, so I've removed it from mine as it doesn't really serve much of a purpose.
PHP functionality: You can now include PHP code into your RSS feed items. Wordpress functions do not work, but there's not much of a reason to add WP functions to the RSS feed.
Any plugin that can display the same content in your feed as it does in your posts will be displayed before and after the RSSupplement items have been placed in your feed if you display the full text. The simple solution is to turn off the feature that adds to your feed and just rely on the one that adds the feature into your post. This is not a problem, however, if you display only the summary.




