[css-text-decor] Use RFC2119 SHOULD.

--HG--
extra : rebase_source : eb123b7b9292743ecfc2369dce4e91bba6a9fc9a

Author: fantasai

css-text-decor/Overview.html

@@ -1126,10 +1126,9 @@ <h3 id=line-position><span class=secno>2.7. </span> Determining the
   </div>
 
   <p>Some font formats (such as OpenType) can offer information about the
-   appropriate position of an underline. The UA is encouraged to use
-   information (such as the underline thickness, or appropriate alphabetic
-   alignment) from the font wherever appropriate. The same applies to line
-   throughs.
+   appropriate position of an underline. The UA should use such information
+   (such as the underline thickness, or appropriate alphabetic alignment)
+   from the font wherever appropriate. The same applies to line throughs.
 
   <p class=note>Typically, OpenType font metrics give the position of an
    ‘<code class=css>alphabetic</code>’ underline; in some cases

css-text-decor/Overview.src.html

@@ -765,7 +765,7 @@ <h3 id="line-position">
 
   <p>Some font formats (such as OpenType) can offer information
     about the appropriate position of an underline.
-    The UA is encouraged to use information (such as the underline thickness,
+    The UA should use such information (such as the underline thickness,
     or appropriate alphabetic alignment) from the font wherever appropriate.
     The same applies to line throughs.