I think you're both confusing things... not sure if it's on purpose or, well... anyhow;
It is common practise for Media Packages (esp. those Commercially Sold) to include all relevant information to those purchasing the Products.
For example when I've done with my Freelance work has been to provide a complete overview of said product.
So for example an Animated Model will breakdown:
• Mesh Components
• Materials / Shaders / Images for each Mesh (Model)
• Rig Outline (along with Tolerances / Joint Types)
• Animation List with (Key) Frame that they exist within
Where-as something like a Sprite Sheet., well generally speaking all Frames within said Sheet are going to be the exact same size; and this will be with both an accompanying readme.txt file
But will also be part of the Sprite Sheet Name.
i.e. Mario_16x16.png
This short-hands what each Sprite Frame is in terms of Size,. then the Sheet is simply broken down into 16x16 Pixel Blocks; and Numerically Assigned (I've noticed in recent years, you tend to NEED to also provide a "Guide" Sheet for how this is broken down)
Essentially the Order is Left > Right., Top > Bottom
So you'd count the number of Frames in a given Animation (provided in the Readme) to figure out what the Sprites will be; and MOST Middleware (Unity / Unreal) will Read Sprite Sheets in this way.
That AppGameKit do this or not... I don't know., honestly I'm fairly sure they outsource all of the Media they sell.
