[css-anchor-position] ||, not &&, as you are allowed to specify just one.

Author: tabatkins

css-anchor-position-1/Overview.bs

@@ -385,7 +385,7 @@ Its syntax is:
 	| x-start | x-end | center-x-start | center-x-end
 	| x-self-start | x-self-end | center-x-self-start | center-x-self-end
 	| all ]
-	&&
+	||
 	[ top | center | bottom | center-top | center-bottom
 	| y-start | y-end | center-y-start | center-y-end
 	| y-self-start | y-self-end | center-y-self-start | center-y-self-end
@@ -394,7 +394,7 @@ Its syntax is:
 	[ block-start | center | block-end | center-block-start | center-block-end
 	| self-block-start | self-block-end | center-self-block-start | center-self-block-end
 	| all ]
-	&&
+	||
 	[ inline-start | center | inline-end | center-inline-start | center-inline-end
 	| self-inline-start | self-inline-end | center-self-inline-start | center-self-inline-end
 	| all ]