How to write validation via regular expression?

Question

Regular Expressions

Tell me, please, who has a regular expression for "you")
For you, this is a common thing, but magic for me)

there is a condition that says:
- the phone number consists of 11 digits (cellular, without spaces, + and any brackets)
- if the first digit 7 or 8, and the second is NOT 9 or 7, then validation passes

Answer 1

/^[78][12345680]\d{9}$/