[css-anchor-position-1] Give pile of algorithms some subheadings w3c#12818

Author: fantasai

css-anchor-position-1/Overview.bs

@@ -4,7 +4,7 @@ Shortname: css-anchor-position
 Level: 1
 Status: ED
 Group: csswg
-Work Status: exploring
+Work Status: refining
 ED: https://drafts.csswg.org/css-anchor-position-1/
 TR: https://www.w3.org/TR/css-anchor-position-1/
 Editor: Tab Atkins-Bittner, Google, http://xanthir.com/contact/, w3cid 42199
@@ -1556,7 +1556,7 @@ Values have the following meanings:
 	: <dfn><<try-tactic>></dfn>
 	::
 		Automatically creates a [=position option=]
-		by [=applying a try-tactic|applying the specified try tactic=]
+		by [=executing a try-tactic|executing the specified try tactic=]
 		to the box's [=base styles=],
 		then adding the constructed [=position option=]
 		to the box's [=position options list=].
@@ -1961,38 +1961,49 @@ This limit must be <em>at least</em> five.
 	all the [=remembered scroll offsets=] stay the same.
 </div>
 
-<div algorithm>
-	To <dfn>apply a position option</dfn> to a box's element |el|,
-	given a [=position option=] |new styles|:
-
-	1. With |new styles| inserted into the cascade
-		in the [=position fallback origin=],
-		resolve the cascade,
-		and perform enough layout to determine |el|'s [=used value|used styles=].
+During a full layout pass,
+once a box has determined its fallback styles
+(or determined it's not using any),
+laying out later boxes cannot change this decision.
 
-		For the purpose of calculating these styles,
-		a <em>hypothetical</em> [=anchor recalculation point=] is calculated,
-		and the resulting hypothetical [=remembered scroll offsets=] are used to determine |el|'s styles.
+<div class=example>
+	For example, say you have two positioned boxes,
+	A and B,
+	with A laid out before B.
+	If B overflows and causes A's containing block to gain scrollbars,
+	this <em>does not</em> cause A
+	to go back and re-determine its fallback styles
+	in an attempt to avoid overflowing.
+	(At best, this can result in exponential layout costs;
+	at worst, it's cyclic and will never settle.)
 
-	2. Return |el|'s [=used value|used styles=].
+	Layout does not "go backward", in other words.
 </div>
 
-<div algorithm="remember or forget the last successful position option">
+<h4 id="statefulness">
+Maintaining and Clearing Fallback Choices</h4>
+
+Some changes to a box have a particularly direct effect on [=determining position fallback styles=]
+and thus trigger special behavior. These <dfn>fallback-sensitive changes</dfn> include:
+	* Its computed 'position' value has changed,
+		its [=containing block=] association has changed,
+		or it no longer generates a box.
+	* Its computed value for any [=longhand property|longhand=] of 'position-try' has changed.
+	* Its computed value for any [=accepted @position-try property=] has changed.
+	* Any of the ''@position-try'' rules referenced by it
+		have been added, removed, or mutated.
+
+In order to maintain layout stability as much as possible,
+[=determining position fallback styles=] prioritizes the [=last successful position option=],
+which is determined as follows:
+
+<div algorithm="record the last successful position option">
 	At the time that {{ResizeObserver}} events are determined and delivered,
-	the box can <dfn export>remember or forget the last successful position option</dfn>:
+	the box must <dfn export>record the last successful position option</dfn> as follows:
 
 	* If |el| has a [=last successful position option=]
 		remove its [=last successful position option=]
-		if any of the following are true:
-
-		* Its computed 'position' value has changed,
-			its [=containing block=] association has changed,
-			or it no longer generates a box.
-		* Its computed value for any [=longhand property|longhand=] of 'position-try' has changed.
-		* Its computed value for any [=accepted @position-try property=] has changed.
-		* Any of the ''@position-try'' rules referenced by it
-			have been added, removed, or mutated.
-
+		if any  [=fallback-sensitive changes=] have occurred.
 		Then, [=determine position fallback styles=] for |el|
 		and set its [=last successful position option=]
 		to the set of [=accepted @position-try properties=] (and values)
@@ -2007,8 +2018,27 @@ This limit must be <em>at least</em> five.
 	is intentionally identical to the treatment of [=last remembered sizes=].
 </div>
 
+<h4 id="applying-options">
+Applying Position Options</h4>
+
+<div algorithm>
+	To <dfn>apply a position option</dfn> to a box's element |el|,
+	given a [=position option=] |new styles|:
+
+	1. With |new styles| inserted into the cascade
+		in the [=position fallback origin=],
+		resolve the cascade,
+		and perform enough layout to determine |el|'s [=used value|used styles=].
+
+		For the purpose of calculating these styles,
+		a <em>hypothetical</em> [=anchor recalculation point=] is calculated,
+		and the resulting hypothetical [=remembered scroll offsets=] are used to determine |el|'s styles.
+
+	2. Return |el|'s [=used value|used styles=].
+</div>
+
 <div algorithm>
-	To <dfn>apply a try-tactic</dfn>
+	To <dfn>execute a try-tactic</dfn>
 	to a set of |styles|
 	of a box's element |el|,
 	between two directions |directions|,
@@ -2124,27 +2154,6 @@ This limit must be <em>at least</em> five.
 	5. Return |styles|.
 </div>
 
-During a full layout pass,
-once a box has determined its fallback styles
-(or determined it's not using any),
-laying out later boxes cannot change this decision.
-
-<div class=example>
-	For example, say you have two positioned boxes,
-	A and B,
-	with A laid out before B.
-	If B overflows and causes A's containing block to gain scrollbars,
-	this <em>does not</em> cause A
-	to go back and re-determine its fallback styles
-	in an attempt to avoid overflowing.
-	(At best, this can result in exponential layout costs;
-	at worst, it's cyclic and will never settle.)
-
-	Layout does not "go backward", in other words.
-</div>
-
-
-
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