add clarification about object data structure (#8447)

* add clarification about object data structure

* improved description with feedback

* fix push of wrong file

docs/docs/general/data-structures.md

@@ -32,6 +32,8 @@ data: [{x:'Sales', y:20}, {x:'Revenue', y:10}]
 
 This is also the internal format used for parsed data. In this mode, parsing can be disabled by specifying `parsing: false` at chart options or dataset. If parsing is disabled, data must be sorted and in the formats the associated chart type and scales use internally.
 
+The values provided must be parsable by the associated scales or in the internal format of the associated scales. A common mistake would be to provide integers for the `category` scale, which uses integers as an internal format, where each integer represents an index in the labels array.
+
 ## Object[] using custom properties
 
 ```javascript