:sig
bool regex_match(String pattern, String subject)
bool regex_match(String pattern, String subject, String flags)

:params
pattern : PCRE2 regular expression pattern
subject : string to test
flags : optional regex flags
return value : `true` when the entire subject matches the pattern

:see
>regex
regex_search
regex_search_all
regex_replace
regex_split
String

:content
Tests whether `subject` matches `pattern` from start to end.

This is a full-string match, not a substring search. Use `regex_search()` when you want to find the first occurrence anywhere in a string.

Examples:

```uce
regex_match("[A-Z][a-z]+", "Alice");      // true
regex_match("[A-Z][a-z]+", "Alice!");     // false
regex_match("\\d{4}-\\d{2}-\\d{2}", "2026-04-29");
```

Supported flags:

- `i` enables case-insensitive matching.
- `m` enables multiline `^` and `$`.
- `s` lets `.` match newlines.
- `x` enables extended / whitespace-insensitive pattern syntax.
- `u` explicitly enables UTF-8 and Unicode character properties.
- `a` disables UTF-8 / Unicode property mode for ASCII-oriented matching.

UCE uses PCRE2 in UTF-8 + Unicode-property mode by default, so patterns such as `\\p{L}+` work naturally on Unicode text.

Invalid patterns or invalid flags raise a request-visible runtime error with the PCRE2 diagnostic message.