[css-align-3] Formally define 'static position rectangle' per WG resolution. w3c#1432 <https://lists.w3.org/Archives/Public/www-style/2018Jul/0028.html>

Author: fantasai

css-align-3/Overview.bs

@@ -2247,6 +2247,60 @@ Aligning Boxes by Baseline</h3>
 	while maintaining baseline alignment within the [=baseline-sharing group=].
 
 
+<h2 id="staticpos-rect">
+ppendix A: Static Position Terminology</h2>
+
+	When both <a>inset properties</a> in a given axis are ''left/auto''
+	on an <a href="https://www.w3.org/TR/CSS2/visuren.html#absolutely-positioned">absolutely positioned box</a>,
+	CSS2 uses its <a>static position</a>
+	to resolve its size and position.
+	See [[css2#abs-non-replaced-width]].
+	The <a>alignment properties</a> modify these calculations,
+	just as they do the sizing and positioning calculations in other layout modes.
+	These modifications refer to a <dfn>static position rectangle</dfn>,
+	whose edges represent the <a>static position</a> of the box
+	from each side of its <a>containing block</a>.
+
+	The <a>static position rectangle</a> and the <a>static positions</a> to which it corresponds
+	are defined by the layout model of its “hypothetical box”:
+
+	<dl>
+		<dt>Block Layout
+		<dd>
+		The <a>static positions</a> of a <a>block-level box</a>
+		are defined in [[CSS2]] Chapter 10.
+		The <a>static position rectangle</a> is a zero-thickness rectangle spanning between
+		the inline-axis sides of the box’s <a>static position containing block</a>
+		(see <a href="https://www.w3.org/TR/CSS21/visudet.html#abs-non-replaced-width">CSS2&sect;10.3.7</a>);
+		and positioned at its <a>block-start</a> <a>static position</a
+		(see <a href="https://www.w3.org/TR/CSS21/visudet.html#abs-non-replaced-height">CSS2&sect;10.6.4).
+
+		<dt>Inline Layout
+		<dd>
+		The <a>static positions</a> of a <a>inline-level box</a>
+		are defined in [[CSS2]] Chapter 10.
+		The <a>static position rectangle</a> is a zero-thickness rectangle spanning between
+		the <a>line-over</a>/<a>line-under</a> sides of the <a>line box</a>
+		that would have contained its “hypothetical box”
+		(see <a href="https://www.w3.org/TR/CSS21/visudet.html#abs-non-replaced-width">CSS2&sect;10.3.7</a>);
+		and positioned at its <a>inline-start</a> <a>static position</a>
+
+		<dt>Flex Layout
+		<dd>
+		The <a>static position rectangle</a> of the child of a <a>flex container</a>
+		corresponds to the <a>content edges</a> of the <a>flex container</a>.
+		See [[!css-flexbox-1#abspos-items]].
+
+		<dt>Grid Layout
+		<dd>
+		By default, the <a>static position rectangle</a> of the child of a <a>grid container</a>
+		corresponds to the <a>content edges</a> of the <a>grid container</a>.
+		However, if that <a>grid container</a> also establishes
+		the box’s actual <a>containing block</a>,
+		then the <a>grid area</a> specified by the <a>grid-placement properties</a>
+		instead establishes its <a>static position rectangle</a>.
+		See [[!css-grid-1#static-position]].
+	</dl>
 
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