5 Unspecified by POSIX, but comparable to @code{strstr}.
9 Portability problems fixed by Gnulib:
12 This function fails to return the start of the haystack for an empty
13 needle on some platforms:
17 This function has quadratic instead of linear complexity on some
22 This function is missing on some platforms:
26 Portability problems not fixed by Gnulib: