Primary source for WoW lua API?
I've been looking for first-hand information on the World of Warcraft addon API. There are a couple wikis that are pretty good, but their reference links only point internally. Surely there is some information published by Blizzard on the topic.
Can all of their information really be gleaned from reverse-engineering and forums? That would be hard for me to believe.
Answer
Its not all necessarily gleaned from inspection or trial and error. Some is provided, but randomly, from "heads up" posts in the forums from "the source", as in Blizzard employees. They are usually pretty good about it, though is almost always provided in a "just the essentials to save you some pain" sort of way.
Here's an example: http://blue.mmo-champion.com/topic/233590-mop-changes/
Watching for the "Blue" posts goes a long way, and its been this way for a long time. If you look at someting like this (old 3.1.0 end user patch notes) http://us.battle.net/wow/en/game/patch-notes/3-1-0 , and then scan to near the bottom there will be a note and link for API changes, so its easy to glean their intent on this, and that they intend to provide some "unofficial" support about API changes there whilenot burdening the actual product readme with them.
In general, I'd say that due to the very open nature of the materials, the source for the UI, very little is hidden and most is pretty self-evident, so it sort of barely qualifies as reverse engineering. Once you understand the Lua relationship to the general design of the WoW UI and supporting API, it's much easier.
As for the implied question about "why", the "hard to believe" part. They are doing, in my estimation, what they believe is the best balance between fully supporting without "officially" suporting, and not wasting cycles trying to document a huge amount of available facilites thats ever changing. I think they belive it makes a better product, having the ability to customize, so its intheir interest, however is frought with problems and even legal issues from many angles to be expressly "official" about it or to try to maintain coherent docs.
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Toward the question "git hub" below, here is the "blue" post in context, which can be found by clicking the "blizz" link icon on the mmo-champion link provided before: http://us.battle.net/wow/en/forum/topic/6413172918#1 I was trying to give an example of a Blue post that had detail, but I accidentally gave one for the Web API not the Game API. However the principle is the same, and provides more Blizzard to Community context for dev support.
So basically that particular post was in reference to changes in the Web API, and the Git remark has no relevance to the game UI Customization and Macro thing. There is no hidden or official doc source for game UI Customization and Macro. Mostly its because it simply doesnt exist for anyone. :)