Joe Touch wrote: > Liberal means that if it's possibly valid, you should accept it as such. That necessitates the protocol designer explicitly flagging some things as invalid. Obvious example is a should be signed message lacking a signature. If taking the most liberal view (as above) the protocol needs to say something like "if the signature is missing or invalid, then the message must be rejected". I don't think that's anything new, I've seen it done. I can see at least the following cases where making intent clear is, in my opinion at least, a good idea: - Security and other sensitive cases of failure. Need to say explicitly reject. - Mechanisms designed for extensions. While the Postel principle makes it unnecessary to say so, it really doesn't hurt saying that a message shouldn't be rejected just for this reason. - Where what you receive is a container of multiple things (messages in a packet, TLVs in a message). Making the assumed dependence/independence clear doesn't hurt (if rejecting/ignoring one, does this impact on the others?). That's not something that spirals out of control in size, a couple of sentences would cover most cases. ******************************************************************** This email and any attachments are confidential to the intended recipient and may also be privileged. If you are not the intended recipient please delete it from your system and notify the sender. You should not copy it or use it for any purpose nor disclose or distribute its contents to any other person. ********************************************************************