BEM modifier separation: underscore or two hyphens?

Question

BEM

Hello.
The official BEM documentation says that the modifier should be separated by an underscore
block_modificator

. But I often see the separation with two hyphens.
block--modificator
And visually, this method seems to me more readable.
There is a temptation to switch to such a designation.
Please help me to understand:
1) Why even "prominent" developers, it turns out, do not follow the documentation, separating the modifier with two hyphens?
2) Is it allowed to use "--" instead of "_"?
Thanks

Answer 1

It is worth reading "Alternative naming schemes"
Here, everyone simply chooses a convenient option for themselves, or the one that is used in your team, for example.
Often code editors are set to a standard naming scheme, so it's more convenient for someone to use it. But everything can be edited if you want.