[Outline Processor Markup Language]

http://www.opml.org/

"Standard" created by Dave Winer for representing an outline as XML. (Out Lining)

Unfortunately it seems an OPML document can't be validated.

• Validation seems like generally a "good thing", but should it be a deal-breaker?

Mark Pilgrim makes a case for out Out Lining format which is mainly ASCII. Because everything in life should be Plain Text. Sure, PyThon code is an outline, and my IDE takes advantage of that. But I don't always have my IDE (it's Ms Windows-specific), and not all installations of EMacs have python-mode. Sometimes all I have is [NotePad]. But Python code is plain text, so I can edit it in anything. All I have to do is keep track of spaces myself; the rest is just text. Simple. This is why I dislike outliners in general, and the OPML format in particular: they presume that my work is primarily an outline, secondarily text. OPML clearly expresses the hierarchical structure of the outline, but obfuscates (entity-encodes) all my actual content. This is exactly backwards.

• OML keeps the node-text bits readable/editable.

The InterOp format for Instant Outlining.

An alternative being explored is OTLML

another is OML

Some code for rendering to a Web Browser.

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