the atr is the string of the first bytes emitted by a contact card following an activation sequence. In an ATR, you have a variable number of interface bytes, then a variable number of historical bytes.
contactless cards don't have ATRs.
ISO 14443-B cards have a PUPI (4 bytes)
ISO 14443-A cards have an UID (4,7 or 10 bytes)
this value is exchanged before the reader reports a fake-ATR.