[css-pseudo-4] Avoid incorrect use of RFC2119 MAY. #4578

Author: fantasai

css-pseudo-4/Overview.bs

@@ -725,7 +725,7 @@ Generated Content Pseudo-elements: ''::before'' and ''::after''</h3>
 
   As with the content of regular elements,
   the generated content of ''::before'' and '':after'' pseudo-elements
-  may be included in any ''::first-line'' and ''::first-letter'' pseudo-elements
+  can form part of any ''::first-line'' and ''::first-letter'' pseudo-elements
   applied to its <a>originating element</a>.
 
 <h3 id="marker-pseudo">