Article from the serie "CCID descriptor statistics"
The bClassEnvelope field is a number value from the USB CCID descriptor:
" Significant only for CCID that offers an extended APDU level for exchanges.
Indicates the default class value used by the CCID when it sends an Envelope command to perform the transportation of an extended APDU by T=0 protocol.
Value FFh indicates that the CCID echoes the class of the APDU. "