Function is_service_valid 

pub fn is_service_valid(pattern: &str) -> bool

Whether a pattern is a valid regular expression that this tool can enforce - i.e. it either compiles directly or compiles after equivalence-preserving normalization / on the backtracking engine. A pattern that is genuinely malformed (unbalanced groups, dangling quantifier the source engine also rejects) returns false. Used by the rule that reports invalid AllowedPatterns so it never fires on a pattern that is merely PCRE-flavored rather than broken.