[css-anchor-1] Move anchor defining sections and expand intro paragraph. w3c#11022

Author: fantasai

css-anchor-position-1/Overview.bs

@@ -145,8 +145,43 @@ For readability they have not been repeated explicitly.
 Like most operations in CSS besides selector matching,
 features in this specification operate over the [=flattened element tree=].
 
-Determining the Anchor {#determining}
-======================
+<h2 id="determining" oldids="determining-position,anchor-position-size">
+Determining the Anchor</h2>
+
+Several features of this specification refer to the position and size of an <dfn local-lt=anchor>anchor box</dfn>.
+Unless otherwise specified,
+this refers to the [=border box=] edge of the [=principal box=] of relevant [=anchor element=].
+In most cases the relevant [=anchor element=] is specified
+as the [=default anchor element=] using the 'position-anchor' property,
+which can refer to an [=implicit anchor element=] defined by the host language
+or an anchor named via the CSS 'anchor-name' and 'anchor-scope' properties.
+(The ''anchor()'' functions can also reference a named anchor directly.)
+
+The [=anchor box=]'s position and size is determined after layout.
+This position and size includes 'zoom' and 'position'-based adjustments
+(such as ''position: relative'' or ''position: sticky'')
+as well as transforms (such as 'transform' or 'offset-path').
+In these cases, the axis-aligned bounding rectangle of the [=anchor box=]
+in the coordinate space of the [=absolutely positioned=] element's [=containing block=]
+is used instead.
+Transforms are often optimized onto a different thread,
+so transform-based updates to an [=anchor box’s=] position
+may be delayed by a few frames.
+Authors can avoid this delay by using absolute or relative positioning instead where practical.
+
+If the [=anchor box=] is [=fragmented=],
+and the [=containing block=] of the [=absolutely positioned=] box
+referring to that [=anchor box=] is outside the relevant [=fragmentation context=],
+the axis-aligned bounding rectangle of its [=box fragments=] is used instead.
+(If the [=absolutely positioned=] box is inside the [=fragmentation context=],
+it sees the [=anchor box=] as unfragmented--
+and can be itself fragmented by the [=fragmentation context=].)
+
+For performance reasons,
+scrolling is handled specially, see [[#scroll]].
+Other post-layout effects, such as filters,
+do not affect the [=anchor box's=] position.
+
 
 <!-- Big Text: a-name
 
@@ -217,57 +252,6 @@ can reference [=anchor names=] defined in “higher” trees.
 Currently, they cannot reference [=anchor names=]
 defined in “lower” shadow trees, though.
 
-### Implicit Anchor Elements ### {#implicit}
-
-Some specifications can define that,
-in certain circumstances,
-a particular element is an <dfn>implicit anchor element</dfn>
-for another element.
-
-<p class=example>
-	TODO: Fill in an example new popover-related details
-	(once that finally lands in the HTML spec).
-
-[=Implicit anchor elements=] can be referenced
-with the ''position-anchor/auto'' keyword in 'position-anchor',
-or by omitting the anchor reference in [=anchor functions=].
-
-The [=implicit anchor element=] of a [=pseudo-element=]
-is its [=originating element=],
-unless otherwise specified.
-
-### The Anchor Box ### {#anchor-position-size}
-
-Several features of this specification refer to the position and size of an <dfn local-lt=anchor>anchor box</dfn>.
-Unless otherwise specified,
-this refers to the [=border box=] edge of the [=principal box=] of the [=anchor element=].
-The [=anchor box=]'s position and size is determined after layout.
-
-This position and size includes 'zoom' and 'position'-based adjustments
-(such as ''position: relative'' or ''position: sticky'')
-as well as transforms (such as 'transform' or 'offset-path').
-In these cases, the axis-aligned bounding rectangle of the [=anchor box=]
-in the coordinate space of the [=absolutely positioned=] element's [=containing block=]
-is used instead.
-Transforms are often optimized onto a different thread,
-so transform-based updates to an [=anchor box’s=] position
-may be delayed by a few frames.
-Authors can avoid this delay by using absolute or relative positioning instead where practical.
-
-If the [=anchor box=] is [=fragmented=],
-and the [=containing block=] of the [=absolutely positioned=] box
-referring to that [=anchor box=] is outside the relevant [=fragmentation context=],
-the axis-aligned bounding rectangle of its [=box fragments=] is used instead.
-(If the [=absolutely positioned=] box is inside the [=fragmentation context=],
-it sees the [=anchor box=] as unfragmented--
-and can be itself fragmented by the [=fragmentation context=].)
-
-For performance reasons,
-scrolling is handled specially, see [[#scroll]].
-Other post-layout effects, such as filters,
-do not affect the [=anchor box's=] position.
-
-
 <!-- Big Text: a-scope
 
  ███▌         ███▌   ███▌   ███▌  ████▌  █████▌
@@ -559,6 +543,25 @@ is the box's <dfn>default anchor box</dfn>.
 	</pre>
 </div>
 
+### Implicit Anchor Elements ### {#implicit}
+
+Some specifications can define that,
+in certain circumstances,
+a particular element is an <dfn>implicit anchor element</dfn>
+for another element.
+
+<p class=example>
+	TODO: Fill in an example new popover-related details
+	(once that finally lands in the HTML spec).
+
+[=Implicit anchor elements=] can be referenced
+with the ''position-anchor/auto'' keyword in 'position-anchor',
+or by omitting the anchor reference in [=anchor functions=].
+
+The [=implicit anchor element=] of a [=pseudo-element=]
+is its [=originating element=],
+unless otherwise specified.
+
 <h3 id=anchor-relevance>
 Anchor Relevance</h3>
 
@@ -2675,8 +2678,9 @@ Significant changes since the <a href="https://www.w3.org/TR/2025/WD-css-anchor-
 	(<a href="https://github.com/w3c/csswg-drafts/issues/12941">Issue 12941</a>)
 * Clarify that ''inset/auto'' 'inset' values are treated as zero when finding the [=inset-modified containing block=] size for 'position-try-order'.
 	(<a href="https://github.com/w3c/csswg-drafts/issues/12942">Issue 12942</a>)
-* Reorganize prose in [[#fallback]] for better readability.
-	(<a href="https://github.com/w3c/csswg-drafts/issues/12811">Issue 12818</a>)
+* Reorganize prose in [[#fallback]] and [[#determining]] for better readability.
+	(<a href="https://github.com/w3c/csswg-drafts/issues/12811">Issue 12818</a>,
+	 <a href="https://github.com/w3c/csswg-drafts/issues/12811">Issue 11022</a>)
 * Improve guidance in [[#accessibility]] and clarify UA requirements.
 	(<a href="https://github.com/w3c/csswg-drafts/issues/10311">Issue 10311</a>)
 * Improve examples.