Address csswg feedback w3c/csswg-drafts#3094 (comment)

source

@@ -112274,8 +112274,8 @@ legend[align=right i] {
 
   <p>The 'fieldset' value is expected to be supported by the '-webkit-appearance' property.</p>
 
-  <p>The 'fieldset' value, when specified on a non-replaced element, is expected to act as
-  follows:</p>
+  <p>The 'fieldset' value, when specified on a non-replaced element (that generates a box, i.e., is
+  not 'display: none' or 'display: contents'), is expected to act as follows:</p>
 
   <ul>
    <li><p>The element is expected to establish a new block formatting context.</p></li>
@@ -112285,15 +112285,13 @@ legend[align=right i] {
 
     <ul>
      <li><p>If the computed value of 'display' is one of 'inline', 'inline-block', 'inline-table',
-     'ruby', 'ruby-base', 'ruby-text', 'ruby-base-container', 'ruby-text-container', then behave as
-     'inline-block'.</p></li>
+     'ruby', 'ruby-base', 'ruby-text', 'ruby-base-container', 'ruby-text-container', 'inline-flex',
+     or 'inline-grid', then behave as 'inline-block'.</p></li>
 
      <li><p>If the computed value of 'display' is one of 'block', 'table', 'table-row-group',
      'table-header-group', 'table-footer-group', 'table-row', 'table-cell', 'table-column-group',
-     'table-column', 'table-caption', 'list-item', 'flow', 'flow-root', or 'run-in', then behave as
-     'block'.</p></li>
-
-     <li><p>Otherwise, use the computed value.</p></li>
+     'table-column', 'table-caption', 'list-item', 'flow', 'flow-root', 'run-in', 'flex', or 'grid',
+      then behave as 'block'.</p></li>
     </ul>
 
     <p class="note">This does not change the computed value.</p>