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Any
Epic uses codes to differentiate objects such as:
However the codes Epic uses by default may not match your working practices. To help with this Epic comes with various alternative formats for each code. There is always a 'manual' option so that codes can be entered by the user. To change the format for a particular code open your user preferences and select 'System Settings / Code Generation'. The options available are displayed:

Note that existing codes are not affected - only codes generated from now on.
If Epic does not offer the code format you require you have two options: