<metathe literal text <meta (case insensitive) \s+any whitespace character, repeated at least once
Non-Capturing Group(?:.*) .*any character (except for line terminators), repeated any number of times
charset=the literal text charset= (case insensitive) "{0,1}?optionally matches the literal " (3410 / 428 / 2216)
.*any character (except for line terminators), repeated any number of times
"{0,1}optionally matches the literal " (3410 / 428 / 2216)
\s*any whitespace character, repeated any number of times
\/{0,1}optionally matches the literal / (4710 / 578 / 2F16)
>the literal > (6210 / 768 / 3E16)
i modifier: insensitive. Matches without distinguishing uppercase and lowercase letters
m modifier: multiline. Causes ^ and $ to match the start and end of each line, not only the start and end of the string
U modifier: Ungreedy. Quantifiers are lazy by default. A trailing ? makes a quantifier greedy