+/* Whether to support address families other than IPv4 in responses which use
+ * the `adns_rr_addr' structure. This is a source-compatibility issue: old
+ * clients may not expect to find address families other than AF_INET in
+ * their query results. There's a separate binary compatibility issue to do
+ * with the size of the `adns_rr_addr' structure, but we'll assume you can
+ * cope with that because you have this header file. Define
+ * `ADNS_FEATURE_IPV4ONLY' if you only want to see AF_INET addresses, or
+ * `ADNS_FEATURE_MANYAF' to allow multiple address families; the default is
+ * currently to stick with AF_INET only, but this is likely to change in a
+ * later release of ADNS.
+ */
+#if !defined(ADNS_FEATURE_IPV4ONLY) && !defined(ADNS_FEATURE_MANYAF)
+# define ADNS_FEATURE_IPV4ONLY
+#elif defined(ADNS_FEATURE_IPV4ONLY) && defined(ADNS_FEATURE_MANYAF)
+# error "Feature flags ADNS_FEATURE_IPV4ONLY and ..._MANYAF are incompatible"
+#endif
+