I want more structure in the file format. OPML is perfect for plain text outliners. But if you want to support rich text then you need to encode the HTML as plain text. This means it's all of the sudden harder to process with web tools like xpath.

Also (not sure this will happen, but I plan to try) I expect to add different node types. For example right now every node is a paragraph. In future might have ... A HEADING (innovation I know). Again that maps really well to HTML, not as well to OPML.

Plus I just like the fact that .bike files are HTML. Makes me confident that they will live and be readable far into the future.

Have you considered using the org format? I'm not saying it'll be good (I've not seen an implementation outside emacs that really gets it) but org-mode has been the best outliner I've personally used.

I haven't looked too much into it. If someone really wanted it and was motivated to help write I would (might, contact me first) support, but generally the existing formats are what I will focus on.

Why not to use markdown formatting?

For example, Dynalist use this idea for their files

And node itself is heading, while when they need paragraph with heading they create _note="" attribute into <outline> element

Markdown is great and I build another app, FoldingText, around it.

But for my own use I over time realized that was a mistake. All the parsing and formatting adds complexity. I think rich text (which to be clear Bike does not yet have, though I will add soon) is a simpler way to work from user perspective. Just issue commands instead of remember and see formatting rules. It's cleaner and simpler for my uses.

I understand, thanks for sharing. I've seen some outliners using node attributes to change how the content is interpreted in OPML and thus being able to use them for things beyond plain-text. I'm quite partial to OPML, but HTML is cool too and easier to reuse.

Anyway, congratulations on the impressive first public release. The more outliners the better in my opinion.