[css-anchor-position-1] Add flip-x and flip-y to position-try-fallbacks #12869

Author: fantasai

css-anchor-position-1/Overview.bs

@@ -1546,7 +1546,7 @@ Values have the following meanings:
 		and adds it to the [=position options list=].
 
 		<pre class=prod>
-		<dfn type><<try-tactic>></dfn> = flip-block || flip-inline || flip-start
+		<dfn type><<try-tactic>></dfn> = flip-block || flip-inline || flip-start || flip-x || flip-y
 		</pre>
 
 		: <dfn>flip-block</dfn>
@@ -1560,6 +1560,17 @@ Values have the following meanings:
 			swaps the values in the [=inline axis=],
 			essentially mirroring across a [=block-axis=] line.
 
+		: <dfn>flip-x</dfn>
+		::
+			swaps the values in the [=horizontal axis=]
+			(between, for example, 'margin-left' and 'margin-right'),
+			essentially mirroring across a [=vertical-axis=] line.
+
+		: <dfn>flip-y</dfn>
+		::
+			swaps the values in the [=vertical axis=],
+			essentially mirroring across a [=horizontal-axis=] line.
+
 		: <dfn>flip-start</dfn>
 		::
 			swaps the values of the [=start=] properties with each other,
@@ -2612,6 +2623,8 @@ Changes {#changes}
 
 Significant changes since the <a href="https://www.w3.org/TR/2025/WD-css-anchor-position-1-20251007/">7 October 2025 Working Draft</a>:
 
+* Add ''flip-x'' and ''flip-y'' to 'position-try-fallbacks'.
+	(<a href="https://github.com/w3c/csswg-drafts/issues/12869">Issue 12869</a>)
 * Define ''anchor-center'' to also use the [=scrollable containing block=]
 	so that it doesn't trigger overflow alignment when positioned outside the [=local containing block=].
 	(<a href="https://github.com/w3c/csswg-drafts/issues/12952">Issue 12952</a>)