[css-overflow] Define module interactions

Author: fantasai

css-overflow-3/Overview.bs

@@ -113,6 +113,14 @@ Value Definitions</h3>
 	also accept the <a>CSS-wide keywords</a> as their property value.
 	For readability they have not been repeated explicitly.
 
+<h3 id="placement">
+Module Interactions</h3>
+
+	This module replaces (supersedes) and extends features defined in [[!CSS2]] section
+	<a href="https://www.w3.org/TR/CSS2/visufx.html#overflow-clipping">11.1 Overflow and clipping</a>
+	and [[!CSS-UI-3]] section
+	<a href="https://www.w3.org/TR/css-ui-3/#text-overflow">5.2. Overflow Ellipsis: the text-overflow property</a>.
+
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css-overflow-4/Overview.bs

@@ -209,6 +209,11 @@ Value Definitions</h3>
 	also accept the <a>CSS-wide keywords</a> as their property value.
 	For readability they have not been repeated explicitly.
 
+<h3 id="placement">
+Module Interactions</h3>
+
+	This module extends features defined in [[!CSS-OVERFLOW-3]].
+
 <h2 id="overflow-concepts">Types of overflow</h2>
 
 	Issue: copy level 3 content when final