[css-display-3] Define “block layout” for convenience.

Author: fantasai

css-display-3/Overview.bs

@@ -954,7 +954,7 @@ Appendix A: Glossary</h2>
 
 		<dt><dfn lt="block-level|block-level content">block-level</dfn>
 		<dd>
-			Content that participates in block layout.
+			Content that participates in [=block layout=].
 			Specifically, block-level boxes.
 
 		<dt><dfn>inline box</dfn>
@@ -1195,6 +1195,11 @@ Appendix A: Glossary</h2>
 			for example, line boxes belonging to the [=inline formatting context=]
 			interact with floats belonging to the [=block formatting context=].
 
+		<dt><dfn>block layout</dfn>
+		<dd>
+			The layout of [=block-level boxes=],
+			performed within a [=block formatting context=].
+
 		<dt><dfn>block formatting context root</dfn>
 		<dd>
 			A <a>block container</a>