What is the RFC compliant and working regular expression to check if a string is a valid URL

Question

There is question by the almost the same name already: What is the best regular expression to check if a string is a valid URL

I don\'t understand this stackoverflow

Answer 1

Here's RFC that you can study: RFC 3986 - Uniform Resource Identifier (URI): Generic Syntax. Section 3.2.2 Host is what you're looking for.

Unfortunately PHP's build-in function filter_var() doesn't support IPv6 syntax: