Minecraft wiki entry for Resource_Pack, associated text: The root tag
 animation: Contains data for the animation
 interpolate: If true, Minecraft generates additional frames between frames with a frame time greater than 1 between them. Defaults to false.
 width: The width of the tile, as a direct ratio rather than in pixels. This is unused in vanilla's files but can be used by resource packs to have frames that are not perfect squares.
 height: The height of the tile as a ratio rather than in pixels. This is unused in vanilla's files but can be used by resource packs to have frames that are not perfect squares.
 frametime: Sets the default time for each frame in increments of one game tick. Defaults to 1.
 frames: Contains a list of frames. Defaults to displaying all the frames from top to bottom.
A number corresponding to position of a frame from the top, with the top frame being 0.
A frame specifies a frame with additional data.
 index: A number corresponding to position of a frame from the top, with the top frame being 0.
 time: The time in ticks to show this frame, overriding "frametime" above.