[css-break-3] Reference fragmentation due to bidi and fragmentation due to block-in-inline splitting from the intro describing box fragments.

Author: fantasai

css-display-3/Overview.bs

@@ -117,8 +117,15 @@ Introduction</h2>
 
 	In the course of layout,
 	<a>boxes</a> and <a>text runs</a> can be broken into multiple <a>fragments</a>.
-	This happens, for example, when an inline box and/or text run is broken across lines,
-	or when a block box is broken across pages or columns.
+	This happens, for example, when an <a>inline box</a> and/or <a>text run</a>
+	is broken across lines,
+	or when a <a>block box</a> is broken across pages or columns,
+	in a process called <a>fragmentation</a>.
+	It can also happen due to bidi reordering of text (see [[css-writing-modes-3#bidi-algo|Applying the Bidirectional Reorderign Algorithm]] in [[css-writing-modes-3#text-direction|CSS Writing Modes]])
+	or higher-level <a>display type</a> box splitting,
+	e.g. <a href="https://www.w3.org/TR/CSS2/visuren.html#img-anon-block">block-in-inline splitting</a>
+	(see <a href="https://www.w3.org/TR/CSS2/visuren.html#box-gen">CSS2&sect;9.2</a>)
+	or <a href="https://www.w3.org/TR/css-multicol-1/#spanning-columns">column-spanner-in-block</a> splitting (see <a href="https://www.w3.org/TR/css-multicol-1/#spanning-columns">CSS Multi-column Layout</a>).
 	A <a>box</a> therefore consists of one or more <a>box fragments</a>,
 	and a <a>text run</a> consists of one or more <a lt=fragment>text fragments</a>.
 	See [[CSS3-BREAK]] for more information on <a>fragmentation</a>.