diff --git a/filter_plugins/domain_relative_to.py b/filter_plugins/domain_relative_to.py
new file mode 100644
index 0000000..72a75e8
--- /dev/null
+++ b/filter_plugins/domain_relative_to.py
@@ -0,0 +1,10 @@
+def domain_relative_to(domain):
+    if domain == '@':
+        return zone
+    if domain[-1] != '.':
+        return f"{domain}.{zone}"
+    return domain
+
+class FilterModule(object):
+    def filters(self):
+        return {'domain_relative_to': domain_relative_to}
diff --git a/filter_plugins/ip_net_rev.py b/filter_plugins/ip_net_rev.py
new file mode 100644
index 0000000..6c2b4fb
--- /dev/null
+++ b/filter_plugins/ip_net_rev.py
@@ -0,0 +1,29 @@
+from netaddr import IPNetwork, IPSet
+
+def ip_rev(orig, rev, net):
+    if orig.isdisjoint(IPSet(net)):
+        rev.add(net)
+        return
+    elif orig.issuperset(IPSet(net)):
+        return
+    else:
+        for net in net.subnet(net.prefixlen + 1):
+            ip_rev(orig, rev, net)
+
+def ip_net_rev(addresses, version=None):
+    orig = IPSet(addresses)
+    rev = IPSet()
+    if version in [None, 4]:
+        ip_rev(orig, rev, IPNetwork('0.0.0.0/0'))
+    if version in [None, 6]:
+        ip_rev(orig, rev, IPNetwork('::/0'))
+    return [str(net) for net in rev.iter_cidrs()]
+
+class FilterModule(object):
+    def filters(self):
+        return {'ip_net_rev': ip_net_rev}
+
+if __name__ == '__main__':
+    import sys
+    for ip in ip_net_rev(sys.argv[1:]):
+        print(ip)
diff --git a/filter_plugins/mapping.py b/filter_plugins/mapping.py
new file mode 100644
index 0000000..6183181
--- /dev/null
+++ b/filter_plugins/mapping.py
@@ -0,0 +1,8 @@
+from collections import Mapping
+
+def mapping(val):
+    return isinstance(val, Mapping)
+
+class FilterModule(object):
+    def filters(self):
+        return {'mapping': mapping}