- * This function can be used to determine which of two similar
- * options will be the one to take effect.
+ * This can also distinguish among multiple synonymous options, such
+ * as "proto=," "udp" and "tcp."
+ *
+ * Returns the index into @keys of the option that is rightmost.
+ * If none of the options listed in @keys is present in @options, or
+ * if @options is NULL, returns -1.