[css-anchor-position] Invalid anchor() or anchor-size() with no fallback is IACVT. #10005

Author: tabatkins

css-anchor-position-1/Overview.bs

@@ -1015,7 +1015,7 @@ only if all the following conditions are true:
 If any of these conditions are false,
 the ''anchor()'' function resolves to its specified fallback value.
 If no fallback value is specified,
-it resolves to ''0px''.
+it makes the declaration referencing it [=invalid at computed-value time=].
 
 
 <!-- Big Text: visibility
@@ -1224,7 +1224,7 @@ only if all the following conditions are true:
 If any of these conditions are false,
 the ''anchor-size()'' function resolves to its specified fallback value.
 If no fallback value is specified,
-it resolves to ''0px''.
+it makes the declaration referencing it [=invalid at computed-value time=].
 
 
 <!-- Big Text: fallback