3.3.1.2 Progressive Tile Contexts
The Progressive Tile Contexts ADM element contains a list of progressive tile contexts. Each progressive tile context is associated with a tile in an off-screen surface and one or more codec contexts stored in the Codec Contexts (section 3.3.1.1) ADM element. The progressive tile context contains the sign state of each coefficient (described as Sign in section 3.3.8.2.1.1) and the bit position for each band (described as BitPos in section 3.3.8.2.1.2).
A progressive tile context can be discarded once all of the codec contexts with which it is associated have been deleted.