[css-gaps-1] Clarify gap intersection point dfn to be consistent with examples.

Author: kbabbitt

css-gaps-1/Overview.bs

@@ -99,10 +99,17 @@ Layout and painting {#layout-painting}
 	the decorations need to scroll along with items in the container.
 
 	A <dfn>gap intersection point</dfn> is defined to exist in each of the following locations:
-	<ul>
-		<li>The center of an intersection between a gap and the content edge of the container.</li>
-		<li>The center of an intersection between gaps in different directions.</li>
-	</ul>
+	<ol>
+		<li>The center of an intersection between a gap and the content edge of the container,
+			unless that intersection is crossed by a spanning item.</li>
+		<li>The center of an intersection between gaps in different directions, excluding:
+			<ol>
+				<li>Intersections where both sides of the same gap are crossed by
+					spanning items adjacent to the intersection.</li>
+				<li>Intersections completely covered by a spanning item.</li>
+			</ol>
+		</li>
+	</ol>
 
 	The following examples illustrate the locations of <a>gap intersection points</a>,
 	marked with a magenta <span style="color:#f0f">+</span> in each case.
@@ -123,8 +130,9 @@ Layout and painting {#layout-painting}
 		<figcaption>
 			Locations of <a>gap intersection points</a> in a grid with spanning items.
 			Note the presence of <a>gap intersection points</a> at edges of the container,
-			and the absence of <a>gap intersection points</a> where adjacent grid items
-			span both sides of what would otherwise be an intersection (#2 and #6, or #4 and #7).
+			except where a spanning item crosses the intersection, such as the top center of #1.
+			Note also the absence of <a>gap intersection points</a> where adjacent grid items
+			span both sides of an intersection, such as between #2 and #6, or #4 and #7.
 		</figcaption>
 	</div>
 
@@ -182,8 +190,9 @@ Breaking gap decorations into segments: The 'column-rule-break', 'row-rule-break
 		</dd>
 		<dt><dfn>none</dfn>
 		<dd>
-			Gap decorations start and end at <a>gap intersection points</a>
-			which are at an edge of the container only.
+			Gap decorations start and end at all intersections between gaps and
+			edges of the container. Spanning items and <a>gap intersection points</a>
+			do not factor into the placement of gap decorations in this mode.
 		</dd>
 	</dl>