rdmap-03 spec clarification

draft-ietf-rddp-rdmap-03.txt, section 6.1:

"Bits 32-63; Invalidate STag. However, this field is only valid
 for Send with Invalidate and Send with Solicited Event and
 Invalidate Messages (see Figure 4 RDMA Usage of DDP Fields).
 For Send, Send with Solicited Event, RDMA Read Request, and
 Terminate, the Invalidate STag field MUST be set to zero on
 transmit and ignored by the receiver."

Could someone tell me if "ignored by the receiver" means 

1) If it is not zero the receiver MUST NOT generate an error
2) The receiver MUST CHECK that the STag is zero but in case it is 
   it does nothing with it.

thanks in advance,

-patricio kaplan