+converts a string representing an octal number to numeric form.
+
+On entry I<start> and I<*len> give the string to scan, I<*flags> gives
+conversion flags, and I<result> should be NULL or a pointer to an NV.
+The scan stops at the end of the string, or the first invalid character.
+Unless C<PERL_SCAN_SILENT_ILLDIGIT> is set in I<*flags>, encountering an
+invalid character will also trigger a warning.
+On return I<*len> is set to the length of the scanned string,
+and I<*flags> gives output flags.
+
+If the value is <= UV_MAX it is returned as a UV, the output flags are clear,
+and nothing is written to I<*result>. If the value is > UV_MAX C<grok_oct>
+returns UV_MAX, sets C<PERL_SCAN_GREATER_THAN_UV_MAX> in the output flags,
+and writes the value to I<*result> (or the value is discarded if I<result>
+is NULL).
+
+If C<PERL_SCAN_ALLOW_UNDERSCORES> is set in I<*flags> then the octal
+number may use '_' characters to separate digits.