[css-gaps-1] Update definition of 'crossing gap width' to be consistent with resolution taken in #12922

Author: kbabbitt

css-gaps-1/Overview.bs

@@ -809,13 +809,21 @@ Adjusting gap decoration endpoints: The 'rule-inset' properties</h3>
 		<dt>
 			Edge segment endpoints
 		<dd>
-			The <a>crossing gap width</a> is ''0''.
+			The [=crossing gap width=] is ''0''.
 
 		<dt>
 			Interior segment endpoints
 		<dd>
-			The <a>crossing gap width</a> is the used value of the 'column-gap' or 'row-gap' property,
-			whichever applies to the intersecting gap.
+			The [=crossing gap width=] is the size of the [=gap junction=]
+			in the same dimension as the [=gap=] in which the [=segment endpoint=] lies
+			(the horizontal dimension for row gaps and the vertical dimension for column gaps).
+
+			Note: Typically, this will be the used value of the 'column-gap' or 'row-gap' property,
+			whichever applies to the intersecting or abutting gap,
+			plus any additional spacing added due to 'justify-content' or 'align-content'.
+			However, in cases where [=gaps=] intersect or abut one another at overlapping intervals,
+			the [=crossing gap width=] will be determined by the union of such intervals.
+			See <a href="#example-unpaired-endpoints-1">this example</a> for one such case.
 	</dl>
 
 	<p>