[css-position-3] Update abstract.

Author: fantasai

css-position-3/Overview.bs

@@ -13,8 +13,7 @@ Previous Version: https://www.w3.org/TR/2012/WD-css3-positioning-20120207/
 Editor: Rossen Atanassov, Microsoft, ratan@microsoft.com, w3cid 49885
 Editor: Arron Eicholz, Microsoft, arronei@microsoft.com, w3cid 37934
 !Issues list: <a href="http://wiki.csswg.org/spec/css-position/">in Wiki</a>
-Abstract:This module contains the features of CSS level&nbsp;3 relating to positioning and stacking of elements. It includes and extends the functionality of CSS level&nbsp;2 ([[!CSS2]]), which builds on CSS level&nbsp;1 [[CSS1]]. The main extensions compared to level&nbsp;2 are the ability to position elements based on CSS Region boxes, the ability to specify different containing blocks for elements and sticky positioning. <p>Other kinds of layout, such as tables, "floating" boxes, ruby annotations, grid layouts, columns and basic handling of normal "flow" content, are described in other modules. Also, the layout of text inside each line is defined elsewhere.
-Ignored Terms: div, dl, dfn, attachment-type, attachment-top, attachment-right, attachment-bottom, attachment-left, attachment, scrolling box
+Abstract: This module contains defines coordinate-based positioning and offsetting schemes of <a href="https://www.w3.org/TR/CSS/">CSS</a>: [=relative positioning=], [=sticky positioning=], [=absolute positioning=], and [=fixed positioning=].
 Link Defaults: css-transforms-1 (property) transform
 </pre>