[css-align-3] Define that justify-self affects automatic sizes the same for block, flex, or grid items. w3c#12102

Author: tabatkins

css-align-3/Overview.bs

@@ -1470,7 +1470,12 @@ Inline-Axis (or Main-Axis) Self-Alignment: the 'justify-self' property</h3>
 		<tr>
 			<th>Other Details
 			<td>
-				In terms of CSS2.1 block-level formatting [[!CSS2]],
+				The [=automatic size=] of a [=block-level box=]
+				whose 'justify-self' is not ''justify-self/normal''
+				is equivalent to ''fit-content''
+				(rather than e.g. ''width/stretch'', as is typical for a [=non-replaced=] [=block-level box=]).
+				Additionally,
+				in terms of CSS2.1 block-level formatting [[!CSS2]],
 				the rules for “over-constrained” computations in <a href="https://www.w3.org/TR/CSS2/visudet.html#blockwidth">section 10.3.3</a>
 				are ignored in favor of alignment as specified here
 				and the used value of the margin properties are therefore not adjusted to correct for the over-constraint.
@@ -2546,6 +2551,9 @@ Changes</h2>
 		(<a href="https://github.com/w3c/csswg-drafts/issues/11937">Issue 11937</a>)
 	* Defined anonymous block boxes to always act like ''justify-self: normal''.
 		(<a href="https://github.com/w3c/csswg-drafts/issues/11461">Issue 11461</a>)
+	* Defined that 'justify-self' affects the [=automatic size=] of block-level boxes
+		the same way it does for flex and grid items.
+		(<a href="https://github.com/w3c/csswg-drafts/issues/12102">Issue 12102</a>)
 
 	See also <a href="https://www.w3.org/TR/2025/WD-css-align-3-20250311/#changes">previous changes</a>.