Comment 2 for bug 1183179

I absolutely don't agree with the above claim. I have, for example, modified the XMLS API to be incompatible at version 2.0. I think that clients that are aware of this, and that don't have time or inclination to update, should be able to say this by providing an upper bound on the version compatibility.

Lots of real systems in the real world end up relying on old versions of libraries, and I don't think it's our job to tell people they can't do this.

Your argument seems to violate your own postulate about having the person who knows specify. In this case, the provider can't know all the consumers. A consumer's programmer can know that the consumer is incompatible with the new API. Why make the poor *users* of the consumer guess what's gone wrong when they try to use the new, shiny, incompatible library? Allow the consumer's programmer to tell his users that they must use the old version.