Fix value definition. Update chapter 4 introduction for height and wrapping. (#12618)

Author: mstensho

css-multicol-2/Overview.bs

@@ -677,19 +677,20 @@ The multi-column model</h2>
 <h2 id="the-number-and-width-of-columns">
 The number and size of columns</h2>
 
-	Finding the number and width of columns is fundamental when laying out multi-column content.
-	These properties are used to set the number and width of columns:
+	Finding the number and size of columns is fundamental when laying out multi-column content.
+	These properties are used to set the number and size of columns:
 
 	<ul>
 		<li>'column-count'</li>
 		<li>'column-width'</li>
+		<li>'column-height'</li>
 	</ul>
 
-	A third property, 'columns',
-	is a shorthand property which sets 'column-width' and 'column-count', and 'column-height'.
+	A fourth property, 'columns', is a shorthand property which sets all of
+        'column-width', 'column-height', and 'column-count'.
 
-	Other factors, such as explicit column breaks, content, and height constraints,
-	may influence the actual number and width of columns.
+	Other factors, such as explicit column breaks, content, column wrapping,
+        and size constraints, may influence the actual number and size of columns.
 
 
 <h3 id='cw'>The Inline Size of Columns: the 'column-width' property</h3>