I'm still pretty new to Lua/XML as a whole. And since there doesn't appear to be much out there in the way of learning it aside from technical documentation, I've just been picking things apart and experimenting to figure out how things work. I've come to notice that there is a lot of API functionality that simply has absolutely no documentation anywhere. In this example namely, HybridScrollFrames (_Update, _GetOffsets and _CreateButton). Is anyone familiar with any sort of documentation explaining how it's used and what it's function parameters are? And how it manipulates XML templates would be bonus. Maybe a very bare-bones example to pick apart? I can only ever find it used in large project AddOns which is a nightmare to search through.
If anyone also has information on the similar functions for FauxScrollFrames that would be amazing as well. I've found documentation to the extent of "FauxScrollFrame_Update(frame, numItems, numToDisplay, valueStep, button, smallWidth, bigWidth, highlightFrame, smallHighlightWidth, bigHighlightWidth)". But I've only ever seen the first 4 parameters actually used in anything. So have no idea what data types are required for, say, highlightFrame (true/false errors out). I imagine it's for mouseovers or select.
Just starting out with scrolling frames myself and I do know that HybridScrollFrames requires you to create an XML template in order to use it. I do not know much about its associated methods, as well as for FauxScrollFrame and it's methods. Currently working with UIPanelScrollBar/UIPanelScrollFrame templates, I have mocked up a working scrolling window using data from my bags, just working on trying to figure out how to update that data without making a mess.
most of the more commonly used methods from the API are documented by the community, but for those that aren't, I usually start with a print(method_name()) and start looking at errors and return values, etc..
I recommend getting the addon Wow Lua, it has a nice in-game editor and it has helped me out immensely, I usually use it for testing and fleshing out functions, etc.
I said I'd make a guide for hybrid scrollframes at some point, but never got around to it. What exactly are you looking to use it for? Just having a single frame with some stuff on it that can be scrolled (long texts or the quest list), or more of a list like your mount collection?
I've never actually used FauxScrollFrames, but I know my way around HybridScrollFrames. So I could cough up a crash course on those.
If you don't mind learning through reading code, you can also check this and this file. They are part of the 8.2.5 PTR do quickly set up a basic HybridScrollFrame. They add some extra complexity through mixins, which aren't needed to make something yourself.