Where to see code for Business Content SAP exit variable?

SAP exit variable are type of BEx variables processed during BEx Query runtime by replacement path predefined in SAP exit. SAP exit is like customer exit it is just delivered by standard SAP BW Business Content. Comparison to customer exit is right since there is also ABAP code which is in particular performing the replacement of variable value.

This might seems to be tricky for first look: Where to see ABAP code for BEx variables a type of SAP exit? Actually again comparing to user exits variable it is stored in ABAP repository but in include just in function modules:

In our case for variable 0P_SYSID there is the function module called RSVAREXIT_0P_SYSID where all the variable logic is coded:

update - 27-09-2012-

Older business content variables (e.g. 0CWD) are coded in FM RREX_VARIABLE_EXIT.