Parses a Tango-style format string fragment. Regex: \{(\d*)\s*([,.]\s*-?\d*\s*)?(:[^}]*)?\}
null if not found, an escaped "{{", or a format string "{...}".
See Implementation
Parses a Tango-style format string fragment. Regex: \{(\d*)\s*([,.]\s*-?\d*\s*)?(:[^}]*)?\}