2G emergency camping b4 normal attach

Would you know if there is a 3GPP spec indicating whether a terminal is required to perform 2G emergency camping (thus no matter the PLMN) before performing a normal attach procedure on a suitable cell on the relevant PLMN?

For instance:
– at power on, is the terminal required to perform an emergency camping FIRST before normal attach if the SIM card is valid ? (in case the SIM is not valid, it is required as far as I know)
– At mode switch from 3G to 2G, is the terminal required to perform FIRST emergency camping or not?

Generally, in 2G, is the emergency camping prior to a normal attach required or left to the developper’s choice?
If it is required by the specs, in which spec references?

Thank you in advance!