[css-lists-3] Follow up wording tweaks to marker intro text.

Author: fantasai

css-lists-3/Overview.bs

@@ -88,24 +88,28 @@ Declaring a List Item</h2>
 <h2 id='markers'>
 Markers</h2>
 
-	The defining feature of the <a>list item</a> <a>display type</a> is its <i>marker</i>,
+	The defining feature of the <a>list item</a> <a>display type</a>
+	is its <dfn lt="marker | marker box">marker</dfn>,
 	a symbol or ordinal that helps denote the beginning of each <a>list item</a> in a list.
-	List item boxes thus generate, in addition to their principal box,
-	a <dfn export lt="marker | marker box">marker box</dfn>
-	(represented by the ''::marker'' pseudo-element)
-	which contains and displays this marker.
+	In the CSS layout model,
+	<a>list item</a> <a>markers</a> are represented by
+	the <a>marker box</a> associated with the <a>list item</a>.
+	The contents of this <a>marker</a> can be controlled with
+	the 'list-style-type' and 'list-style-image' properties on the <a>list item</a>
+	and by assigning properties to its ''::marker'' pseudo-element.
 
 <h3 id='marker-pseudo'>
 The ''::marker'' Pseudo-Element</h3>
 
-	The <a>marker box</a> generated by the ''::marker'' pseudo-element of a <a>list item</a>
-	is generated as the first child of the <a>list item</a>,
+	The <a>marker box</a> is generated by
+	the ''::marker'' pseudo-element of a <a>list item</a>
+	as its first child,
 	before the ''::before'' pseudo-element
-	(if it exists on the element)
-	and filled with content
+	(if it exists on the element).
+	It is filled with content
 	as defined in [[#content-property]].
 
-	<a>Marker boxes</a> only exist on <a>list items</a>;
+	<a>Marker boxes</a> only exist for <a>list items</a>:
 	on any other element,
 	the ''::marker'' pseudo-element's 'content' property must compute to ''content/none'',
 	which suppresses its creation.