+JSON Map object containing subdomain names as its keys and domain
+objects as values. Element of the map with empty key "" has special
+meaning: the value of this map element is merged into the current
+domain object. This operaton happens first when a new domain object
+is analyzed, and is performed recursively. In the result of the
+merge, the `"map"` does not contain the element with empty key.
+Further operatons that can potentially modify the contents of the
+current domain object (`import` and `delegate` lookups) start when
+the empty element of the `"map"` has been recursively merged into
+the current object.
+
+```
+"map": { "www": { "alias" : "www.example.com" }
+ , "www2": { "delegate": "d/example" }
+ }
+```
+
+Note: When a key contains dots ".", it is converted to a nested
+map. If empty element appears as a result of split, such as when
+a dot is at the beginning or at the end of the key, or there are
+consequitive dots, such elemets are ignored. For example,
+
+```
+"map": { "www.uk": { "alias" : "www.example.co.uk" }
+ , "www..us": { "alias" : "www.example.com" }
+ , "smtp.us.": { "alias" : "smtp.example.com" }
+```
+
+is equivalent to
+
+```
+"map": { "uk": { "map": { "www": { "alias" : "www.example.co.uk" }}}
+ , "us": { "map": { "www": { "alias" : "www.example.com" }
+ , "smtp": { "alias" : "smtp.example.com" }}
+ }
+ }
+```