This technical corrigendum to ITU-T Rec. X.691 | ISO/IEC 8825-2:
a) clarifies the PER visibility of pattern constraints;
b) clarifies the encoding of the length determinant when the type is constrained and has an upper bound greater than or equal to 64K and the UNALIGNED variant of PER is in use;
c) clarifies the behaviour of compound subtype constraints that involve permitted alphabet constraints.