add since version

Author: cmeissner

docs/filters.rst

@@ -8,6 +8,8 @@ is_subnet
 
 This filter checks wether a given subnet belongs to the second one. It returns `true` if first subnet belongs to second and `false` if not or both subnets are the same.
 
+**since version:** 1.2.0
+
 .. code-block:: yaml
 
    192.0.2.0/25 | codeaffen.phpipam.is_subnet(192.0.2.0/24)