Without further ado, the following was found:

Issue:    behaviour → behavior  (according man-pages(7) american English is used)

"By default, B<getopt>()  permutes the contents of I<argv> as it scans, so "
"that eventually all the nonoptions are at the end.  Two other scanning modes "
"are also implemented.  If the first character of I<optstring> is \\[aq]+\\"
"[aq] or the environment variable B<POSIXLY_CORRECT> is set, then option "
"processing stops as soon as a nonoption argument is encountered.  If \\[aq]+"
"\\[aq] is not the first character of I<optstring>, it is treated as a normal "
"option.  If B<POSIXLY_CORRECT> behaviour is required in this case "
"I<optstring> will contain two \\[aq]+\\[aq] symbols.  If the first character "
"of I<optstring> is \\[aq]-\\[aq], then each nonoption I<argv>-element is "
"handled as if it were the argument of an option with character code 1.  "
"(This is used by programs that were written to expect options and other "
"I<argv>-elements in any order and that care about the ordering of the two.)  "
"The special argument \"--\" forces an end of option-scanning regardless of "
"the scanning mode."