Your comment says this can't be done. It can, the syntax is undocumented.

[tieniber]

I'm referring to here:

mendix-DataTables/src/DataTables/DataTables.xml

Line 46 in cc61d11

<!--property key="attr" type="attribute" entityProperty="tableEntity" This does not work! Error: entity cannot be resolved>

You just have to specify the entity property like this:
entityProperty="../tableEntity"
So you're indicating that you need to traverse up one level to get to that entity property. Hope that helps!

[mgroeneweg]

Good to know the feature is actually there. However, Mendix is quite busy pruning any undocumented stuff while updating the documentation on the official features. So I will not use this feature until it is clear that it is here to stay.

Thanks for the heads-up anyway,

[tieniber]

Turns out this actually is documented:

Per: https://github.com/mendix/docs/blob/development/content/refguide/xml-reference-guide.md

entityProperty:
Assigns a entity to a property. This should point to the key attribute of the entity to which it is related. This could also be relative (like "../entityName") when the attribute is inside a object list:

[mgroeneweg]

LOL! That's new. Well it does sound like a great idea however it would also break existing usage of the widget so I probably need to add the new properties while deprecating the old stuff to allow migration.
I will reopen this issue, probably a nice one when adding new functionality.