File flags are transparently converted between a bitmap representation and a textual format. For example, if you set the bitmap and ask for text, the library will build a canonical text format. However, if you set a text format and request a text format, you will get back the same text, even if it is ill-formed. If you need to canonicalize a textual flags string, you should first set the text form, then request the bitmap form, then use that to set the bitmap form. Setting the bitmap format will clear the internal text representation and force it to be reconstructed when you next request the text form.
The bitmap format consists of two integers, one containing bits that should be set, the other specifying bits that should be cleared. Bits not mentioned in either bitmap will be ignored. Usually, the bitmap of bits to be cleared will be set to zero. In unusual circumstances, you can force a fully-specified set of file flags by setting the bitmap of flags to clear to the complement of the bitmap of flags to set. (This differs from fflagstostr(3), which only includes names for set bits.) Converting a bitmap to a textual string is a platform-specific operation; bits that are not meaningful on the current platform will be ignored.
The canonical text format is a comma-separated list of flag names. The archive_entry_copy_fflags_text_w function parses the provided text and sets the internal bitmap values. This is a platform-specific operation; names that are not meaningful on the current platform will be ignored. The function returns a pointer to the start of the first name that was not recognized, or NULL if every name was recognized. Note that every name--including names that follow an unrecognized name--will be evaluated, and the bitmaps will be set to reflect every name that is recognized. (In particular, this differs from strtofflags(3), which stops parsing at the first unrecognized name.)
XXX This needs serious help. XXX
An "Access Control List" (ACL) is a list of permissions that grant access to particular users or groups beyond what would normally be provided by standard POSIX mode bits. The ACL handling here addresses some deficiencies in the POSIX.1e draft 17 ACL specification. In particular, POSIX.1e draft 17 specifies several different formats, but none of those formats include both textual user/group names and numeric UIDs/GIDs.
XXX explain ACL stuff XXX