Description of FcStrDirname is absent in the official documentation of
fontconfig-2.5.92. At the same time the source documentation contains
description of the function.
The problem is a consequence of a misprint in the format of the source
documentation file 'fcstring.fncs'. The finish mark of description of the
previous function is absent.
FcStrCopyFilename constructs a canonical path for any argument, including
expanding leading ~ and editing '.' and '..' elements out of the resulting
path.