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A behind-the-scenes look at Radio UserLand attributes Intro  After yesterday's DaveNet piece I've been getting questions about the attributes in an element in OPML and how that relates to attributes in Radio UserLand. The purpose of this tutorial is to walk you through the way Radio UserLand manages these attributes. Tutorial  One of the simplest types is a link, this nodetype is talked about extensively in yesterday's DaveNet. Screen 1. To create a link, first open any outline and press Return to create a new headline. Type in a short name, and then press Enter to finish the headline. Screen 2. To link this headline to another outline, choose Add Link from the Radio menu, enter this url. Screen 3. To see the attributes that are invisibly attached to the headline, right-click on it, and choose the Debug command. Screen 4. A table opens, showing two attributes, type and url. Screen 5. Looking at the OPML generated for this outline, there's a single element in the , and it has the same attributes as shown in Screen 4. There's always a one-one mapping of attributes in RU and the attributes in the OPML file. Screen 6. Now back to what the user sees. When I expand the link, all the top-level elements from my history file are filled in. This is the "virtuality" that I talk about in the DaveNet piece. Going deeper  The UserLand outliner has had the ability to store information invisibly on each outline node, probably since version 1.0. Menubar objects use this feature, to link from an outline item to a script. (This is the reason menubars can't have attributes, not a big loss, imho.) In version 7.0 we formalize that and put a structure on that information. Attributes are stored in a table containing as many Frontier objects as the programmer wants to put there. There are new verbs for accessing these attributes, and an open architecture for creating your own types. If you're a Frontier guru, check out the nodetypes page, esp the scenario-in-a-screenshot. Newsfeeds are nodes with links to RSS files that expand in-place, much as OPML documents do.

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