As described in the example about Attribute Codes, adding the identical [key] to multiple Codes allows you to enter all these Codes at once.
If you want to log e.g. three different Codes (in three different Classes) while pressing a single [key], setup your Code definitions like this:
▪Click Start - Observation - Define Codes 
to open the Code definitions dialog.
▪Assign three Codes and Classes to the same [key], like this:
If now [*] is pressed, while logging Events, one single Event is created, containing all four three that were assigned to key [*] in the corresponding Classes:
This can be useful, to add an aggregated version of the detailed Codes used for logging.
▪Read Chains of communication and Attribute Codes for a practical implementation.