language vs implementation limits

Tab, If there isn't already language like you indicate below in some
generic guideline/requirement in one or more of the CSS specs, then perhaps
it could be added?

G.

---------- Forwarded message ----------
From: <bugzilla-daemon@webkit.org>
Date: Tue, Nov 20, 2012 at 1:19 PM
Subject: [Bug 102735] Clamp out-of-range numbers in CSS
To: glenn@skynav.com

https://bugs.webkit.org/show_bug.cgi?id=102735


--- Comment #15 from Tab Atkins <tabatkins@google.com>  2012-11-20 12:21:43
PST ---
(In reply to comment #14)
> Just an FYI, but CSS specs are not presently consistent regarding
clamping versus ignoring. For example, CSS3 Animation requires a keyframe
declaration outside of 0-100% to be ignored and not merely clamped to 0 or
100. See https://bugs.webkit.org/show_bug.cgi?id=96844.

Again, as I explained, the rule is that *language-defined limits* cause
things to be ignored.  It's a syntax error, since you know about it
beforehand and everyone is the same (barring bugs).

We clamp when we encounter *implementation-defined limits*, because they're
unspecified and variable across time and browsers, so there's no way for
authors to robustly protect themselves from violating the limit.

The behavior of keyframes is consistent with this.  (If you do know of any
inconsistencies, please report them on www-style so we can try to fix them!)