I'm sure you know what HTML is. But what about OPML? BlogHer Hobbies editor Debra Roby says it makes her think of Oompa Loompas. It reminds me of my two-year-old's request for "opa-meal" at breakfast time. OPML stands for Outline Processor Markup Language, a human-readable text format for managing hierarchical, ordered lists. It's most commonly used to manage lists of RSS feed subscriptions, but it could easily be used for other applications, like to do list management or saving a playlist of music. If you export subscriptions from the Web-based news reader Bloglines, you'll get an OPML file. OPML is big these days because people who read lots of blogs are looking for better ways to manage the information overload that often results from subscribing to too many feeds. OPML is a foundational technology for addressing that.

The person most closely associated with OPML is Dave Winer, whose UserLand software company developed OPML as a file format for an outlining package. Now Dave's building the OPML Editor, a desktop tool for creating and manipulating OPML files. It's beta right now, but if you're interested in trying it out, download it now. The OPML Editor includes a blogging tool that allows for quick and easy mini-posts grouped by date. You can check out my OPML blog to see what such a blog looks like.

Lisa Williams and Amy Bellinger are two women to watch in OPML. Lisa blogs at Learning The Lessons of Nixon; H2otown.info, a blog devoted to issues in her local community of Watertown, Massachusetts; and at OPML Fan, her OPML blog. Amy blogs at learnandteachonline.com and on her experimental OPML blog. They're both working hard lately to help get the OPML Editor ready for a Version 1.0 release, complete with video tutorials, community blog, and user documentation.

The OPML Editor is not by any means the only tool available to manipulate OPML. OPML is a text format, so you could always create and modify it using any old text editor. But a host of other possibilities exist. Towards the end of last year, Amy Gahran of Contentious wrote up her own thoughts on OPML in Using OPML for Thinking, Writing, Publishing, crediting BlogHer Feminism & Gender editor Koan Bremner for introducing it to her. Shortly thereafter, Amy discovered the OPML Manager. She calls it "a pretty easy way to put your OPML files online in a web-rendered form. That is, you don't just see the ugly code - when you upload your OPML file, you actually see topics and subtopics that you can click on to expand or collapse."

Bela Labovitch of RSSLabs helps develop OPMLSearch and OPMLWorkstation, two other tools that are useful if you want to use OPML. OPML Search provides for a Google-like search of online OPML files while OPML Workstation is a Web-based application for managing and publishing OPML files.

Have you heard of OPML reading lists? That's just a way for people to subscribe to a list of feeds rather than the feeds themselves. It's implemented as a dynamic OPML file living at a URL. Though this isn't well-supported by current newsreaders (BlogBridge is one exception), it's an exciting possibility for the future. I'd love it if I could subscribe to the BlogHer Tech & Web blogroll as a reading list, offered as an OPML file located at a specific URL. Then when new blogs were added or defunct ones removed, my news reader would automatically see the changes without my having to do anything.