[css-position-3] Fix broken definition of static position rectangle.

Author: fantasai

css-position-3/Overview.bs

@@ -767,20 +767,18 @@ Absolute (and Fixed) Positioning</h3>
 
 
 <h4 id="staticpos-rect">
-Resolving Automatic Insets</h4>
+Resolving Automatic Insets: the “Static Position Rectangle”</h4>
 
 	When both [=inset properties=] in a given axis are ''left/auto'',
-	they are resolved in reference to the box’s
-	<dfn export lt="static-position rectangle|static position rectangle">static-position rectangle</dfn>,
-	whose edges represent the [=static position=] of the box
-	from each side of its [=containing block=].
-	This [=static-position rectangle=]
-	and the [=static positions=] to which it corresponds
-	are defined by the layout model
-	the box would have had if its 'position' were ''position/static''
-	(and its 'float' and 'clear' values were ''float/none'').
-	(Note that this may require assuming a different hypothetical value
-	for 'display' as well.)
+	they are resolved into a <dfn>static position</dfn>
+	by aligning the box into its <dfn>static-position rectangle</dfn>,
+	an [=alignment container=] derived
+	from the [=formatting context=] the box would have participated in
+	if it were ''position: static''
+	(independent of its actual containing block).
+	The [=static position=] represents
+	an approximation of the position the box would have had
+	if it were ''position: static''.
 
 	<dl>
 		<dt>Block Layout
@@ -826,12 +824,15 @@ Resolving Automatic Insets</h4>
 			See the <a href="https://www.w3.org/TR/css-grid-1/#static-position">static position of a grid container child</a> in [[!CSS-GRID-1]].
 	</dl>
 
-	For the purposes of calculating the [=static-position rectangle=],
-	the [=containing block=] of [=fixed positioned=] elements
-	is the [=initial containing block=] instead of the [=viewport=],
+	Finding the [=static position=] and the [=static position rectangle=]
+	assumes that both 'float' and 'clear' have their initial values,
+	and can require assuming a different hypothetical value
+	for 'display' as well.
+	Additionally, the [=containing block=] of [=fixed positioned=] elements
+	is assumed to be the [=initial containing block=] instead of the [=viewport=],
 	and all [=scroll containers=] should be assumed
 	to be scrolled to their [=initial scroll position=].
-	Additionally, all ''margin/auto'' margins on the box itself
+	Lastly, all ''margin/auto'' margins on the box itself
 	are treated as zero.
 
 <h4 id="abspos-breaking" oldids="breaking">