The Internationalization Module’s support for regular expressions is based primarily on UTR-18 Version 5.1. However, the module also provides support for much of UTR-18 Version 6 (http://www.unicode.org/reports/tr18/).

Support for Version 6 includes all Level 1, 2, and 3 features, except for other properties, intersection, tailored properties, element-level loose matches, and fine-grained Level 3 support. While Version 6 places support for surrogates at Level 1, The Internationalization Module provides that support at Level 2, in keeping with the guidelines from UTR-18 Version 5.1.