Function is_capture_char

regex/regex-syntax/src/ast/parse.rs:112–115

Returns true if the given character is a valid in a capture group name. If `first` is true, then `c` is treated as the first character in the group name (which is not allowed to be a digit).

(c: char, first: bool)

/// If `first` is true, then `c` is treated as the first character in the
/// group name (which is not allowed to be a digit).
fn is_capture_char(c: char, first: bool) -> bool {
    c == '_' || (!first && c >= '0' && c <= '9')
    || (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z')
}

/// A builder for a regular expression parser.
///