merange values in x264?

[Forteen88]

I wonder, which are valid merange values in x264?
I've seen people mostly use 16, 24, 32, 48
but is it OK to use 28?

EDIT: OK, thanks for the detailed answer DS.

[Dark Shikari]

Anything works, but:

DIA/HEX clip to between 4 and 16.
HEX rounds up to mod2.
UMH rounds up to mod4 for the UMH section and mod2 for the HEX section.
ESA/TESA round up to mod4.