Can't you use flags in regular expressions in the pattern attribute?

Question

HTML

Something did not find complete documentation about the pattern attribute.
This is how validation works pattern="^[А-ЯЁ][А-ЯЁа-яё]*?-?[А-ЯЁа-яё]+$"
But not like this pattern="/^[А-ЯЁ][А-ЯЁа-яё]*?-?[А-ЯЁа-яё]+$/g"
How to use regular expression flags?