The purpose of the story is to make it much easier for developers to add a button to the Online Editor that inserts a custom tag they have created.

At the moment (1.11), adding a button requires changes to core files, as well as a subsantial javascript file, configuration and CSS. Once we have agreed on the UI for custom tags, it should be fairly easy to automate the addition of such a button.

Given the name and properties of a custom tag, all buttons have the same behaviour. The icon and help text are specific to each tag.

Open questions

Unless I'm mistaken, there are client side tools to "theme" the OE, and enable a set of button or another. It would be more optimal, maybe, to use that feature to choose which buttons appear and where.

In any case, it is important that a maintainer has full freedom about the buttons that show up.

Even though it ain't limited to the buttons, autoconfiguration should be used as much as possible for those tags. For instance, the CSS or icon for a custom tag could be picked based on a standardized path (platform/oe/custom_tags for instance).