Add note to 3.3.2 understanding to explain "require" in normative wording (#4367)

Closes #4214

See also #2357 (comment)

Co-authored-by: Scott O'Hara <[email protected]>
Co-authored-by: Mike Gower <[email protected]>

Author: 3 people

understanding/20/labels-or-instructions.html

@@ -59,7 +59,11 @@ <h2>Intent of Labels or Instructions</h2>
       <p>While this success criterion requires that controls and inputs have labels or instructions, whether or
          not labels (if used) are accurate, sufficiently clear, or descriptive is covered separately by
          <a href="headings-and-labels">2.4.6: Headings and Labels</a>.
-      </p> 
+      </p>
+      <p class="note">The use of "requires" in this criterion's normative wording does not mean that the criterion only applies
+         to <em>required</em> form fields. It is used here as a synonym for "accepts", "expects", or "allows". The criterion
+         applies to all form fields, whether they're required or optional.
+      </p>
 
    </section>
    <section id="benefits">
@@ -87,8 +91,8 @@ <h2>Examples of Labels or Instructions</h2>
 
       <ul>
 
-         <li>A field which requires the user to enter the two character abbreviation for a US state
-            has a link next to it which will popup an alphabetized list of state names and the
+         <li>A field which asks the user to enter the two character abbreviation for a US state
+            has a link next to it which will pop up an alphabetized list of state names and the
             correct abbreviation.
          </li>