+/* Parses 'arg' as a set of arguments to the "learn" action and appends a
+ * matching NXAST_LEARN action to 'b'. The format parsed is described in
+ * ovs-ofctl(8).
+ *
+ * Prints an error on stderr and aborts the program if 'arg' syntax is invalid.
+ *
+ * If 'flow' is nonnull, then it should be the flow from a cls_rule that is
+ * the matching rule for the learning action. This helps to better validate
+ * the action's arguments.
+ *
+ * Modifies 'arg'. */