Merge pull request #1567 from telefonicaid/task/add-doc-special-attr-names

[Doc] Add special measures and attributes names

Author: fgalan

doc/api.md

@@ -8,6 +8,7 @@
     -   [IoT Agent information model](#iot-agent-information-model)
         -   [Config groups](#config-groups)
         -   [Devices](#devices)
+    -   [Special measures and attributes names](#special-measures-and-attributes-names)
     -   [Entity attributes](#entity-attributes)
     -   [Multientity support)](#multientity-support)
     -   [Metadata support](#metadata-support)
@@ -149,6 +150,15 @@ This behavior allows that autoprovisioned parameters can freely established modi
 creation using the provisioning API. However, note that if a device (autoprovisioned or not) doesn't have these
 parameters defined at device level in database, the parameters are inherit from config group parameters.
 
+## Special measures and attributes names
+
+In case of arriving measures with name `id` or `type`, they are automatically transformed to `measure_id` and 
+`measure_type` attributes at Context Broker update. The reason behind this is to avoid to collide with the original entity ID and type, as mechanism 
+that enable store measure values from parameters called with the same name. It only applies to autoprovisioned
+attributes and is also available at JEXL context with the same name (`measure_id`or `measure_type`).
+
+In case of provisioning attributes using `id` or `type` as names (please don't do that ;), they are ignored. 
+
 ## Entity attributes
 
 In the config group/device model there are four list of attributes with different purpose to configure how the