bearclaw supports plugins. plugins are html documents that may or may not contain their own CSS or JS.
think of it like a "template" you can stick anywhere.
plugins should be added to the plugins folder as a .zip. bearclaw will automatically extract the zip and put it where it needs to go.
plugins normally contain html files, so let's say you have a page-hit counter that goes up every time a new person shows up. let's call it "pagehits". your plugin would arrive as pagehits.zip which you'd drop in to the bearclaw/plugins folder.
run bearclaw, and that zip file will turn itself into a folder with some html files inside, in this example lets say it is today.html and total.html. today.html shows you how many hits your page had today, and total.html has how many hits your page has in total.
To call a plugin in your markdown pages, use a plugin comment like this:
<!-- plugin "./plugins/pagehits/total.html" -->
in our pagehits example, this should auto-insert our total page hits plugin every time we run bearclaw. bearclaw will try and rebuild everything in markdown folder every time it is run.