Applications may either install a message catalog in the MO format as specified by the info page in version 0.10.40 of the gettext source package, or the application may execute the msgfmt command during it's installation to compile the message catalog. In either case, the resulting output must be located in the package's private area under /opt, and the application may use bindtextdomain() to specify this location.
Implementations shall support the POSIX and C locales as specified in the Single UNIX Specification.
Utilities that process regular expressions shall support Basic Regular Expressions and Extended Regular Expressions as specified in the Single UNIX Specification, with the following exceptions:
Range expression (such as [a-z]) can be based on code point order instead of collating element order.
Equivalence class expression (such as [=a=]) and multi-character collating element expression (such as [.ch.]) are optional.
Handling of a multi-character collating element is optional.