[cssom-view] Make the various scrolling algorithms accept a pseudo-element.

Author: tabatkins

cssom-view-1/Overview.bs

@@ -412,9 +412,11 @@ This specification depends on the WHATWG Infra standard. [[!INFRA]]
 
 <h3 id=scrolling>Scrolling</h3>
 
+<div algorithm="perform a scroll of a box">
+
 When a user agent is to <dfn export>perform a scroll</dfn> of a <a>scrolling box</a> <var>box</var>,
 to a given position <var>position</var>,
-an associated element <var>element</var> and optionally a scroll behavior <var>behavior</var>
+an associated element or [=pseudo-element=] <var>element</var> and optionally a scroll behavior <var>behavior</var>
 (which is "<code>auto</code>" if omitted),
 the following steps must be run:
 
@@ -434,6 +436,10 @@ the following steps must be run:
   Note: If the scroll position did not change as a result of the user interaction or programmatic invocation, where no translations were applied as a result, then no <a event>scrollend</a> event fires because no scrolling occurred.
 </ol>
 
+</div>
+
+<div algorithm="perform a scroll of a viewport">
+
 When a user agent is to <dfn for="viewport" export>perform a scroll</dfn> of a <a>viewport</a> to a given position <var>position</var> and optionally a scroll behavior <var>behavior</var>
 (which is "<code>auto</code>" if omitted) it must perform a coordinated viewport scroll by following these steps:
 
@@ -464,6 +470,8 @@ so that the layout viewport is scrolled before the visual viewport. This is done
 reasons to ensure consistent scroll event ordering. See the <a href="#example-vvanimation">example
 above</a> for a visual depiction.
 
+</div>
+
 <div class='example'>
     The user pinch-zooms into the document and ticks their mouse wheel, requesting the user agent scroll the document down by 50px. Because the document
     is pinch-zoomed in, the visual viewport has 20px of room to scroll. The user agent distributes the scroll by scrolling the visual viewport down by
@@ -1445,8 +1453,9 @@ The <dfn attribute for=Element>currentCSSZoom</dfn> attribute must return the
 
 <h3 id=element-scrolling-members>{{Element}} Scrolling Members</h3>
 
+<div algorithm>
 
-To <dfn export>determine the scroll-into-view position</dfn> of a <var>target</var>, which is an <a for="/">Element</a> or <a>Range</a>,
+To <dfn export>determine the scroll-into-view position</dfn> of a <var>target</var>, which is an <a for="/">Element</a>, [=pseudo-element=], or <a>Range</a>,
 with a scroll behavior <var>behavior</var>,
 a block flow direction position <var>block</var>,
 an inline base direction position <var>inline</var>,
@@ -1497,9 +1506,10 @@ run the following steps:
             <dd>Align <var>element edge D</var> with <var>scrolling box edge D</var>.
         </dl>
     1. Return <var>position</var>.
+</div>
 
-
-To <dfn export>scroll a target into view</dfn> <var>target</var>, which is an <a for="/">Element</a> or <a>Range</a>,
+<div algorithm>
+To <dfn export>scroll a target into view</dfn> <var>target</var>, which is an <a for="/">Element</a>, [=pseudo-element=], or <a>Range</a>,
 with a scroll behavior <var>behavior</var>,
 a block flow direction position <var>block</var>,
 and an inline base direction position <var>inline</var>,
@@ -1522,9 +1532,11 @@ a <a>scrolling box</a> <var>scrolling box</var>, in order of innermost to outerm
             1. <a for="viewport">Perform a scroll</a> of the <a>viewport</a> to <var>position</var>, with <var>root element</var> as the associated element and <var>behavior</var>
                 as the scroll behavior.
     </dl>
+</div>
 
+<div algorithm>
 
-To <dfn>scroll an element</dfn> <var>element</var> to <var>x</var>,<var>y</var> optionally with a scroll behavior <var>behavior</var> (which is "<code>auto</code>" if omitted) means to:
+To <dfn>scroll an element</dfn> (or [=pseudo-element=]) <var>element</var> to <var>x</var>,<var>y</var> optionally with a scroll behavior <var>behavior</var> (which is "<code>auto</code>" if omitted) means to:
 
 1. Let <var>box</var> be <var>element</var>'s associated <a>scrolling box</a>.
 1. <dl class=switch>
@@ -1544,7 +1556,7 @@ To <dfn>scroll an element</dfn> <var>element</var> to <var>x</var>,<var>y</var>
 1. Let <var>position</var> be the scroll position <var>box</var> would have by aligning <a>scrolling area</a> x-coordinate <var>x</var> with the left of <var>box</var> and aligning <a>scrolling area</a> y-coordinate <var>y</var> with the top of <var>box</var>.
 1. If <var>position</var> is the same as <var>box</var>'s current scroll position, and <var>box</var> does not have an ongoing <a>smooth scroll</a>, abort these steps.
 1. <a for="/">Perform a scroll</a> of <var>box</var> to <var>position</var>, <var>element</var> as the associated element and <var>behavior</var> as the scroll behavior.
-
+</div>
 
 
 <h2 id=extensions-to-the-htmlelement-interface>Extensions to the {{HTMLElement}} Interface</h2>