@var{bitlen} has to be a multiple of 8.
@item str @var{len}
-Unibyte string (@pxref{Text Representations}) of length @var{len}.
+Unibyte string (@pxref{Text Representations}) of length @var{len} bytes.
When packing, the first @var{len} bytes of the input string are copied
to the packed output. If the input string is shorter than @var{len},
the remaining bytes will be null (zero) unless a pre-allocated string
following is true:
@itemize
@item
-The input string is shorter than @var{len} and either no pre-allocated
+The input string is shorter than @var{len} bytes and either no pre-allocated
string was provided to @code{bindat-pack} or the appropriate byte in
the pre-allocated string was already null.
@item