And content limits. Why can't my password contain the % character? No special characters? What makes a character "special"? Why can't it contain emoji? So many password systems go to great lengths to remove potential entropy and randomness from passwords with their rules. The usual excuse is "blah blah blah legacy systems" which is not a good reason.

Personally, I wouldn't use anything beyond ASCII in a password. I don't want encoding bugs to lock me out of my encrypted partition or bank account, thank you very much.