If you are wondering what Dimensions can be used to map and group data from any of your data sources made in a Funnel account, just navigate to the Dimensions tab in the left side navigation:

Scroll past your list of Custom Dimensions, and a list of all the native Dimensions will follow. These are the Dimensions that you can use to build your Custom Dimensions on!
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Alternatively, you can use the Search function. Just type the data source type.