[web-animations-1][web-animations-2][editorial] Mention that we need to define the overridden implicit keyframe generation behavior from scroll animations

See #2081.

Author: birtles

web-animations-1/Overview.bs

@@ -4062,6 +4062,21 @@ Keyframe effects {#keyframe-effects}
       and a [=composite operation=] of [=composite operation add|add=],
       and append it to the end of |property-specific keyframes|.
 
+  <div class=note>
+
+    Other specifications may override
+    the implicit keyframe generation behavior
+    in the preceding two steps.
+    For example, the
+    [[scroll-animations-1#named-range-keyframes|named timeline range keyframe selectors]]
+    defined by Scroll Animations
+    can cause these implicit keyframes not to be generated.
+
+    A future level of this specification should
+    incorporate the overridden behavior directly into this algorithm.
+
+  </div>
+
   1. Let |interval endpoints| be an empty sequence of keyframes.
 
   1. Populate |interval endpoints| by following the steps
@@ -4213,40 +4228,6 @@ Keyframe effects {#keyframe-effects}
     produced by the transition on 'font-size'.
   </div>
 
-  <div class=issue>
-    In the presence of certain easing functions,
-    the input [=iteration progress=] to an animation effect
-    is not limited to the range [0, 1].
-    Currently, however, keyframe offsets <em>are</em> limited to the range [0, 1]
-    and property values are simply extrapolated
-    for input [=iteration progress=] values outside this range.
-
-    We have considered removing this restriction
-    since some cases exist where it is useful
-    to be able to specify non-linear changes in property values
-    at [=iteration progress=] values outside the range [0, 1].
-    One example is an animation that interpolates from green to yellow
-    but has an overshoot easing function
-    that makes it temporarily interpolate “beyond” yellow to red
-    before settling back to yellow.
-
-    While this effect could be achieved by
-    modification of the keyframes and easing function,
-    this approach seems to break the model's separation
-    of timing concerns from animation effects.
-
-    It is not clear how this effect should be achieved
-    but we note that allowing keyframe offsets outside [0, 1]
-    can make the currently specified behavior,
-    where keyframes at offset 0 and 1 are synthesized as necessary,
-    inconsistent.
-
-    See <a href="http://lists.w3.org/Archives/Public/public-fx/2013AprJun/0184.html">section 4
-    (Keyframe offsets outside [0, 1]) of minuted discussion from Tokyo 2013 F2F</a>.
-
-    <a href="https://github.com/w3c/csswg-drafts/issues/2081">&lt;https://github.com/w3c/csswg-drafts/issues/2081&gt;</a>
-  </div>
-
 Combining effects {#combining-effects}
 -----------------
 <div class=informative-bg>

web-animations-2/Overview.bs

@@ -2136,6 +2136,14 @@ Update the description of an effect that targets a non-animated property as:
 
 <h4 id="the-effect-value-of-a-keyframe-animation-effect">The effect value of a keyframe effect</h4>
 
+Issue: The implicit keyframe generation steps in Web Animations Level 1
+need to be reconciled with the behavior defined for
+[[scroll-animations-1#named-range-keyframes|named timeline range keyframe selectors]]
+in Scroll Animations.
+Scroll Animations currently overrides those steps but that overridden behavior
+should be incorporated directly in this algorithm.
+See <a href="https://github.com/w3c/csswg-drafts/issues/14309">issue 14309</a>.
+
 The procedure for computing the <a>effect value</a> of a single property
 referenced by a <a>keyframe effect</a> as one of its <a>target properties</a>,
 for a given <var ignore=''>iteration progress</var>, <var>current iteration</var> and