[css-logical] List keywords correctly. Add dfn.

Author: fantasai

css-logical-1/Overview.bs

@@ -172,9 +172,10 @@ Value Definitions</h3>
 <h2 id="directional-keywords">
 Flow-Relative Values: <css>block-start</css>, <css>block-end</css>, <css>inline-start</css>, <css>inline-end</css></h2>
 
-  Properties that accept physical directional keyword values
-  ('top', 'bottom', 'left', or 'right') are redefined
-  to also accept the appropriate <a>flow-relative</a> directional keywords.
+  Properties that accept [=physical=] <dfn>directional keyword</dfn> values
+  (<css>top</css>, <css>bottom</css>, <css>left</css>, <css>right</css>)
+  are redefined to also accept the appropriate <a>flow-relative</a> [=directional keywords=]
+  (<css>block-start</css>, <css>block-end</css>, <css>inline-start</css>, <css>inline-end</css>).
   In such cases,
   the flow-relative values can be used in place of the corresponding physical values.
   For properties that take multiple keywords,
@@ -183,7 +184,8 @@ Flow-Relative Values: <css>block-start</css>, <css>block-end</css>, <css>inline-
 
   Properties can be either 1-dimensional or 2-dimensional.
   When contextually constrained to one dimension,
-  the flow-relative keywords are abbreviated.
+  the flow-relative keywords are abbreviated
+  (to <css>start</css> and <css>end</css>).
 
 <h3 id="caption-side">
 Logical Values for the 'caption-side' Property</h3>