When ever you bookmark a pdf or doc item in del.icio.us it is displayed in a system tag page (so not only does your new item show up in your account and the del.icio.us home page , but it is also displayed in the pdf or doc page)
…it does this by adding an invisible tag.
Next time you bookmark a pdf, go to this page and you will also see it there (by bookmarking it is automatically added to a page that lists only pdf files, as the tag “system:filetype:pdf” is automatically added without you knowing)
…you will notice that the bookmark in your account will not have the system tag, only the other tags you applied, as the system tag is invisible.
NOTE: related link - Yummy is a social bookmanager that is devoted entirely to only pdf files.
Check out this post from the del.icio.us blog to see the other many system tags…the bookmarks in the system media tags (such as audio and video files) automatically have enclosures.
NOTE: related link - see this post to add enclosures to your own del.icio.us tags.
This is building a collection of bookmarks by filetype…del.icio.us could really display these systems pages on their homepage so people are aware of them.
Shadows displays UberTags on their homepage as kind of a system tag, but this is more of a displayed communal tag as opposed to a system tag, (and you have to manually apply the UberTag to your bookmark, it’s not automatic).
Now if you subscribe to the RSS mp3 system tag you will get the lastest bookmarks downloaded straight into your RSS Reader (must read enclosures)
You can add a tag “+” with a system tag so you can refine your selections
eg. subscribe to an RSS feed of the mp3 system tag plus the tag “jazz”…see here (it still stays as a podcast feed)
…or even do this with an artist, say Madonna.
But this means someone had to tag the bookmark with the Madonna tag, what if there are other Madonna mp3’s in the del.icio.us system but they aren’t tagged “Madonna”, how do we get to them, for example they might be under the tag “pop”.
Well instead of combining tags, maybe you could create a search feed with the mp3 system tag feed (ie. filter or re-mix the feed)
How do we do this?
Put the feed into ReFilter, add your search term, and check out your new customised feed…problem is that I assume that it will not be a podcast feed, so you’ll have to go to Feedburner to enable it…see here.
I wonder if you could have system tags at the user level, that way you could subscribe to your friends del.icio.us mp3 bookmarks without them even tagging the bookmark with an mp3 tag, as its done automatically.