[css-values-5] Force the random base value to stay in the [0, 1) range.

Author: tabatkins

css-values-5/Overview.bs

@@ -2115,6 +2115,12 @@ Generating a Random Numeric Value: the ''random()'' function</h3>
 			rather than allowing the UA to generate a [=random base value=]
 			and controlling how it's shared.
 
+			While ''1'' is technically allowed as a valid value
+			(because CSS grammars can only express closed ranges),
+			the [=random base value=] is clamped to the highest representable value
+			less than ''1'',
+			so [=random base values=] remain in the half-open range `[0, 1)`.
+
 			Note: While this <em>might</em> be useful for authors
 			to get predictable values while testing a page,
 			the reason it exists is to fix some corner cases in [=inheritance=]