MVC, add note for non common fieldtypes

source/development/frontend/models.rst

@@ -113,9 +113,19 @@ From top to bottom we find the following nodes in our tree:
 -  someText, not part of the entity tag and also defined as text without
    validation
 
-The fieldtypes are easily extendable in the base system and they all live in
+The fieldtypes are easily extendable in the base system and all common ones live in
 their own namespace at *OPNsense\\Base\\FieldTypes* deriving from *BaseField*.
 
+.. Note::
+
+   When designing application specific fieldtypes, you can point to a field
+   type within the application namespace using a full or partial path. 
+
+   For example using *Vendor\\Component\\FieldTypes\\MyFieldType* to point to a specific non
+   common field type or *.\\MyFieldType* when linked from the application model itself (which assumes a namespace FieldTypes
+   exists)
+
+
 -------------
 Usage example
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