d2s_spec_keyvalue_mapping.md

@@ -3,11 +3,19 @@
 ## Introduction
 Devices send key-value data in the format described [here](https://git.falcom.de/pub/wiki/wikis/d2s_spec_sfal_dataframe).
 
-comes in as typeless key-value pairs.
-Visualization of these data in the frontend  
+These data, even if following some special format definitions, come in in a typeless form.
+To visualize these data in the frontend, one of the key features of the mapping engine is to define the underlying format of the incoming data, e.g. key1="1.23" would suggest the type DOUBLE as the mapping type inside a mapping definition. Attaching a human readable name is another benefit from the mapping. So properly named in the mapping definition a key as e.g. _temp could be mapped to a more readable form as temperature.
+
+The most interesting feature comes in with the description of an optional formula, which can convert any incoming values and formats on-the-fly to more meaningful values. The underlying framework used for these calculations is [mXparser](http://mathparser.org/). D2Sphere uses a more or less the complete subset out of these features, even that some format restrictions come into place.
 
 ## Specification
 
+- The outgoing key can be named differently from the incoming one, e.g. _accl_x vs. formula $[N(0)]_accl$ * 10;
+
+## Restrictions
+
+Even if the incoming value (or parts of it in case of a vecotr) can be used more than once inside the same formula, there is currently no support for different incoming values inside one formula!
+
 ## Examples
 
 ```