alt Hacker NewsNo, its not a "required"... It means someone may have reasons not to use something, and so spec implementors need to allow for circumstances where it is not present.
Those reasons can be anything. Legal, practical, technological, ideaological. You don't know. All you know is not using it is explicitly permitted.
> You don't know. All you know is not using it is explicitly permitted.
In theory, if they are truly following the specification, you know they thought hard about all the consequences.
I think the pushback in the comments comes from the commonsense feeling that this... didn't happen here.