[css-flexbox] Clarify that Box Alignment supercedes Flexbox definitions

Author: fantasai

css-flexbox/Overview.bs

@@ -1740,12 +1740,16 @@ Alignment</h2>
 	including some things that were very difficult in CSS 2.1,
 	like horizontal and vertical centering.
 
-	Note: While the alignment properties are defined in <a href="https://www.w3.org/TR/css3-align/">CSS Box Alignment</a>,
+	Note: While the alignment properties are defined in <a href="https://www.w3.org/TR/css3-align/">CSS Box Alignment</a> [[!CSS-ALIGN-3]],
 	Flexible Box Layout reproduces the definitions of the relevant ones here
 	so as to not create a normative dependency that may slow down advancement of the spec.
 	These properties apply only to flex layout
 	until <a href="https://www.w3.org/TR/css3-align/">CSS Box Alignment Level 3</a> is finished
 	and defines their effect for other layout modes.
+	Additionally, any new values defined in the Box Alignment module
+	will apply to Flexible Box Layout;
+	in otherwords, the Box Alignment module, once completed,
+	will supercede the definitions here.
 
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