Sorry for delay, NeilO, I've been away.
Interesting question, but not for the obvious reason.
First, I say again, that this change in the validation of rule names should have been prominently signalled. It is arbitrary annoying and the fact the non-compliant names still work shows it to have been unnecessary - maintenance work for work's sake?
Second, this UI pretended to accept my commit without providing any indication that it was really doing nothing because of an error.
Third it is possible that the UI turned the border of the offending field red. If so then it is yet another of the UI's that shows this popular mistake - a clear indication of ignorant and inconsiderate designers with no adequate supervision. Like up to 8% of men I am red-green blind and this business of indicating an error by turning a thin line red is almost invisible to me. People thinking about accessibility tend to concentrate on more unusual and more serious sensory defects, but really any UI that signals anything important by a colour change alone is badly designed and shoudl be ashamed of itself.
This whole area of the web mail system looks like the product of an inexperienced team lacking an adult in the room.
In case I need to say it my answer to your question about whether the rule name box turned red is "why should I care".
