[css-anchor-position] Move/rephrase the explanatory note a little to …

…make it more obvious.

css-anchor-position-1/Overview.bs

@@ -297,6 +297,20 @@ that should match an 'anchor-name' value elsewhere on the page,
 or the keyword ''implicit'',
 or nothing (a missing specifier).
 
+Note: The general rule captured by these conditions
+is that an element can only be an anchor
+if it's fully laid out
+before the positioned element that wants to reference it
+is laid out.
+CSS's layout rules provide some useful guarantees about this,
+depending on the anchor and positioned element's relationship
+with each other and their containing blocks.
+The list of conditions below
+exactly rephrases the stacking context rules
+into just what's relevant for this purpose,
+ensuring there is no possibly circularity
+in anchor positioning.
+
 <div algorithm>
  To determine the <dfn>target [=anchor element=]</dfn>
  given a querying element |query el|
@@ -339,17 +353,6 @@ or nothing (a missing specifier).
  which can affect what elements can be [=anchor elements=]
  for a given lookup.
 
- Note: The general rule captured by these conditions
- is that |el| must be fully laid out
- before |query el| is laid out.
- CSS's rules about the layout order of stacking contexts
- give us assurances about this,
- and the list of conditions above
- exactly rephrases the stacking context rules
- into just what's relevant for this purpose,
- ensuring there is no possibly circularity
- in anchor positioning.
-
  Note: An 'anchor-name' defined by styles in one [=shadow tree=]
  won't be seen by [=anchor functions=] in styles in a different [=shadow tree=],
  preserving encapsulation.