Stab at simplifying the linebreaking/flexbox-main-size steps.

Author: tabatkins

css3-flexbox/Overview.html

@@ -1833,10 +1833,31 @@ <h2 id=layout-algorithm><span class=secno>7. </span> Flexbox Layout
      lines:</p>
 
     <ol>
-     <li>Determine the main size of the flexbox's content box.
-      <p class=issue>Fill in the details about how to do so when the width is
-       min/max/fit-content. This is complicated for multiline, especially for
-       &lsquo;<code class=css>flex-flow:column</code>&rsquo;!
+     <li>
+      <p>Determine the maximum line length, based on the main size of the
+       flexbox:</p>
+
+      <dl>
+       <dt>
+
+       <dt>size doesn't rely on its contents
+
+       <dd>The maximum line length is main size of the flexbox's content box.
+
+       <dt>&lsquo;<code class=css>min-content</code>&rsquo;
+
+       <dd>The maximum line length is the flexbox's minimum main size.
+
+       <dt>&lsquo;<code class=css>max-content</code>&rsquo;
+
+       <dd>The maximum line length is the flexbox's maximum main size, or
+        infinity if it has no maximum main size.
+
+       <dt>&lsquo;<code class=css>fit-content</code>&rsquo;
+
+       <dd>Same as if the flexbox was sized as &lsquo;<code
+        class=css>fill-available</code>&rsquo;.
+      </dl>
 
      <li>Collect as many consecutive flexbox items as possible, starting from
       the first item, while keeping the sum of their main size smaller than
@@ -1850,12 +1871,14 @@ <h2 id=layout-algorithm><span class=secno>7. </span> Flexbox Layout
       have been collected into flexbox lines.
     </ol>
 
-   <li>
-    <p>Find the actual main size of the flexbox, per the standard rules for
-     blocks (for block flexboxes) or inline-blocks (for inline flexboxes).</p>
+    <p class=issue>Define "size doesn't rely on its contents". This should be
+     any &lt;length>, a &lt;percentage> that can be resolved, or &lsquo;<code
+     class=css>fill-available</code>&rsquo;.</p>
 
-    <p class=issue>Address min/max/fix-content here as well. Perhaps just
-     combine this step with the previous?</p>
+   <li>Find the actual main size of the flexbox. If the flexbox's main size
+    doesn't rely on its contents, it's actual main size is calculated per the
+    appropriate rules. Otherwise, its main size is the length of its longest
+    line.
 
    <li>For each flexbox line, <a
     href="#resolve-the-flexible-lengths"><i>resolve the flexible

css3-flexbox/Overview.src.html

@@ -898,22 +898,34 @@ <h2 id='layout-algorithm'>
 			<p>If the flexbox is multi-line, group the flexbox items into multiple lines:</p>
 
 			<ol>
-				<li>Determine the main size of the flexbox's content box.
+				<li>
+					<p>Determine the maximum line length, based on the main size of the flexbox:</p>
 
-				<p class='issue'>Fill in the details about how to do so when the width is min/max/fit-content. This is complicated for multiline, especially for ''flex-flow:column''!</p></li>
+					<dt>
+						<dt>size doesn't rely on its contents</dt>
+						<dd>The maximum line length is main size of the flexbox's content box.</dd>
+
+						<dt>''min-content''</dt>
+						<dd>The maximum line length is the flexbox's minimum main size.</dd>
+
+						<dt>''max-content''</dt>
+						<dd>The maximum line length is the flexbox's maximum main size, or infinity if it has no maximum main size.</dd>
+
+						<dt>''fit-content''</dt>
+						<dd>Same as if the flexbox was sized as ''fill-available''.</dd>
+					</dt>
+				</li>
 
 				<li>Collect as many consecutive flexbox items as possible, starting from the first item, while keeping the sum of their main size smaller than the flexbox's available space.  If a flexbox item is sized with a flexible length, then for the purpose of this step, clamp the item's size between its minimum and maximum main sizes.  The items so collected form a single flexbox line.</li>
 
 				<li>Repeat the previous step, starting each time from the first flexbox item not yet collected into a flexbox line, until all flexbox items have been collected into flexbox lines.</li>
 			</ol>
-		</li>
 
-		<li>
-			<p>Find the actual main size of the flexbox, per the standard rules for blocks (for block flexboxes) or inline-blocks (for inline flexboxes).</p>
-
-			<p class='issue'>Address min/max/fix-content here as well.  Perhaps just combine this step with the previous?</p>
+			<p class='issue'>Define "size doesn't rely on its contents". This should be any &lt;length>, a &lt;percentage> that can be resolved, or ''fill-available''.</p>
 		</li>
 
+		<li>Find the actual main size of the flexbox.  If the flexbox's main size doesn't rely on its contents, it's actual main size is calculated per the appropriate rules.  Otherwise, its main size is the length of its longest line.</li>
+
 		<li>For each flexbox line, <i>resolve the flexible lengths</i> of the items contained within it.  All flexbox items now have a final main size.  Update each item's hypothetical cross size based on this main size.</li>
 
 		<li>For each flexbox line, align the flexbox items per 'flex-pack'.  The leftover free-space for each line is calculated by subtracting the sum of the main sizes of the flexbox items on the line from the main size of the flexbox's content box.</li>