Problems:

1. The term “sub-block” is not clearly defined. The clause “which is an array of 16 transform coefficient levels at locations ( xC, yC )” refers to the the transform block, not the sub-block, and is incorrect. Moreover, “(xC, yC)” is not referenced in the coded_sub_block_flag semantics and is not needed.

2. There is a missing comma in “( xS, yS ) is equal to ( LastSignificantCoeffX >> 2 LastSignificantCoeffY >> 2 )”

Proposed Fixes:

1. Indicate that the sub-block is 4x4 and remove the clause “which is an array of 16 transform coefficient levels at locations ( xC, yC )” since it is not needed
2. Add the missing comma