[css-variables-1][editorial] Add a little more context to the case-sensitivity note.

Author: tabatkins

css-variables-1/Overview.bs

@@ -137,10 +137,21 @@ Defining Custom Properties: the '--*' family of properties</h2>
 	if they are [=identical to=] each other.
 
 	<div class='example'>
-		While both '--foo' and --FOO are valid,
-		they are distinct properties -
+		While both '--foo' and '--FOO' are valid,
+		they are distinct properties --
 		using ''var(--foo)'' will refer to the first one,
 		while using ''var(--FOO)'' will refer to the second.
+
+		Perhaps more surprisingly,
+		<css>--fo&#x00f3;</css> and <css>--foo&#x0301;</css> are distinct properties.
+		The first is spelled with U+00F3 (LATIN SMALL LETTER O WITH ACUTE)
+		while the second is spelled with an ASCII "o" followed by U+0301 (COMBINING ACUTE ACCENT),
+		and the "[=identical to=]" relation uses direct codepoint-by-codepoint comparison
+		to determine if two strings are equal,
+		to avoid the complexities and pitfalls of unicode normalization and locale-specific collation.
+
+		Different OSes or input methods can sometimes output visually-identical text with different codepoints,
+		so authors should be aware of this potential hazard.
 	</div>
 
 	Custom properties are <strong>not</strong> reset by the 'all' property.