[css-flexbox-1] Rearrange the definiteness bullets. Slightly rephrase the one about flex container main-size definiteness. Add additional condition about flex-basis definiteness to fix w3c#4311. Remove extraneous note, replace with different useful note.

Author: tabatkins

css-flexbox-1/Overview.bs

@@ -2751,31 +2751,30 @@ Definite and Indefinite Sizes</h3>
 	Although CSS Sizing [[!CSS-SIZING-3]] defines <a spec=css-sizing>definite</a> and <a spec=css-sizing>indefinite</a> lengths,
 	Flexbox has several additional cases where a length can be considered <dfn noexport lt="definite|definite size|indefinite|indefinite size">definite</dfn>:
 
-	<ol>
-		<li>
-			If a <a>single-line</a> <a>flex container</a> has a definite <a>cross size</a>,
-			the  [=automatic size|automatic=] [=preferred size|preferred=] [=outer size|outer=] [=cross size=]
-			of any <a>stretched</a> <a>flex items</a>
-			is the flex container's inner <a>cross size</a>
-			(clamped to the <a>flex item</a>’s min and max <a>cross size</a>)
-			and is considered <a>definite</a>.
-
-		<li>
-			If the <a>flex container</a> has a <a>definite</a> <a>main size</a>,
-			a <a>flex item</a>’s post-flexing <a>main size</a>
-			is treated as <a>definite</a>,
-			even though it can rely on the <a>indefinite</a> sizes
-			of any flex items in the same line.
-
-		<li>
-			Once the cross size of a flex line has been determined,
-			the cross sizes of items in auto-sized flex containers
-			are also considered definite for the purpose of layout;
-			see <a href="#algo-stretch">step 11</a>.
-	</ol>
-
-	Note: The main size of a <a>fully inflexible</a> item with a <a>definite</a> <a>flex basis</a>
-	is, by definition, <a>definite</a>.
+	1. If the [=flex container=] has a [=definite=] [=main size=],
+		then the post-flexing [=main sizes=]
+		of its [=flex items=]
+		are treated as [=definite=].
+
+	2. If a [=flex-item’s=] [=flex basis=] is [=definite=],
+		then its post-flexing [=main size=] is also [=definite=].
+
+	3. If a <a>single-line</a> <a>flex container</a> has a definite <a>cross size</a>,
+		the  [=automatic size|automatic=] [=preferred size|preferred=] [=outer size|outer=] [=cross size=]
+		of any <a>stretched</a> <a>flex items</a>
+		is the flex container's inner <a>cross size</a>
+		(clamped to the <a>flex item</a>’s min and max <a>cross size</a>)
+		and is considered <a>definite</a>.
+
+	4. Once the cross size of a flex line has been determined,
+		the cross sizes of items in auto-sized flex containers
+		are also considered definite for the purpose of layout;
+		see <a href="#algo-stretch">step 11</a>.
+
+	Note: This means that within [=flex layout=],
+	“definite” sizes can require performing layout.
+	This was done to allow percentages inside of [=flex items=]
+	to resolve where authors expected them to resolve.
 
 
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