Ok, so it's a piece of cake to track an individual tag in del.icio.us in your aggregator - while looking at any tag page in del.icio.us (http://del.icio.us/tag/mp3 for instance) you'll see an RSS button all the way down at the bottom. Alternatively, you can just stick an "rss" in any URL before the /tag/, like this: http://del.icio.us/rss/tag/mp3.
But what if you want to get an RSS feed for a search that you've performed - a combination of tags? According to the RSS help page on del.icio.us, you can do that very easily if you want to see a combination within one user's account, but not across the service.
This question was posted to the Web4Lib discussion group, and I thought I'd tackle it using a service called Feed43, which allows you to create an RSS feed from a page where one doesn't natively exist. (I first looked at Feed43 back in March when I was trying to build feeds for wiki pages). It took me about 20 minutes to get the syntax just right, but that's only 'cause I didn't stop to look at the example. I believe the following item search pattern will work with any search performed in del.icio.us:
So where do you stick that? Let's walk through an example. The original request was to get an RSS feed for the search information seeking. So on the Feed43 service, we start with that URL (click images for full size):
Then the tricky part (for me) was looking through the HTML code to figure out the extraction rule for the search pattern (above). Basically you're figuring out which fields repeat for each item in order to suck out the good stuff that you want to appear in your feed, so that goes in the Item Search Pattern:
Finally, I reversed two of the items to get a nice order on the title, URL, description and tags:
The end result for the above search is the following URL: http://feed43.com/del-infoseek.xml You can plug that in your aggregator and be notified of any new search results within del.icio.us.
What's interesting is that a search within del.icio.us doesn't seem to be limited to the tags field, so this example actually finds things that have been tagged with information and with seeking, but also things that haven't been tagged with either tag, but which have both of those words in the title or description of the item being tagged...
Now, this example will work for anything you want to search in del.icio.us, with one caveat! You can't just grab the URL from the browser bar - you have to grab one of the showing 10,25,50 items per page (100 won't work) from down in the lower left corner of your search results screen. Use THAT URL within Feed43, use the code and template order above, and you should be all set.
Having gone through all that, I see that in many instances you can simply combine tags with a + and use the /rss/ trick and get pretty similar (though not identical) results. So for instance, the feed URL of http://del.icio.us/rss/tag/information+seeking will get you pretty similar results.
The feed I built also include the tags that folks used to describe the item and how many other people have tagged it, which are not available in the feed offered by del.icio.us, so that's a bonus :-)