Add note about logo/logotypes contrast to 1.4.3, 1.4.6, and 1.4.11 understanding

understanding/20/contrast-enhanced.html

@@ -126,7 +126,19 @@ <h2>Intent of Contrast (Enhanced)</h2>
          in charts, graphs, diagrams, and other non-text-based information, which is covered by
          <a href="non-text-contrast">Success Criterion 1.4.11 Non-Text Contrast</a>.         
       </p>
-
+
+      <div class="note">
+         <p>Text used as part of a logo or logotype is exempted from contrast requirements,
+            under the assumption that logos/logotypes must comply with stricter color choices mandated
+            by corporate identity guidelines.
+            However, this can be problematic when the logo or logotype also acts as a
+            <em>user interface component</em> (such as a link or other interactive control).
+            In these cases, authors should choose a variant of the logo or logotype that has sufficient
+            contrast, if allowed by the corporate identity guidelines.
+            Alternatively, authors should provide an equivalent <em>user interface component</em>
+            which serves the same purpose and does meet the contrast requirements.</p>
+      </div>
+
       <section>
 
          <h3>Rationale for the Ratios Chosen</h3>

understanding/20/contrast-minimum.html

@@ -130,7 +130,19 @@ <h2>Intent of Contrast (Minimum)</h2>
       <p>See also 
          <a href="contrast-enhanced">1.4.6: Contrast (Enhanced)</a>.
       </p>
-
+
+      <div class="note">
+         <p>Text used as part of a logo or logotype is exempted from contrast requirements,
+            under the assumption that logos/logotypes must comply with stricter color choices mandated
+            by corporate identity guidelines.
+            However, this can be problematic when the logo or logotype also acts as a
+            <em>user interface component</em> (such as a link or other interactive control).
+            In these cases, authors should choose a variant of the logo or logotype that has sufficient
+            contrast, if allowed by the corporate identity guidelines.
+            Alternatively, authors should provide an equivalent <em>user interface component</em>
+            which serves the same purpose and does meet the contrast requirements.</p>
+      </div>
+
       <section>
 
          <h3>Rationale for the Ratios Chosen</h3>

understanding/21/non-text-contrast.html

@@ -396,6 +396,19 @@ <h4>Required for Understanding</h4>
 					<li> The information is available in another form, such as in a table that follows the graph, which becomes visible when a "Long Description" button is pressed.</li>
 					<li> The graphic is part of a logo or brand name (which is considered &quot;essential&quot; to its presentation).</li>
 				</ul>
+
+				<div class="note">
+					<p>Logos and logotypes are exempted from contrast requirements when they are purely used as
+						<em>graphical objects</em>, under the assumption that they must comply with stricter color choices mandated
+            by corporate identity guidelines.
+						However, this is not the case when they also act as <em>user interface components</em>
+						(such as links or other interactive controls). In these cases, authors should choose
+						a variant of the logo or logotype that has sufficient contrast, if allowed by the
+						corporate identity guidelines.
+						Alternatively, authors should provide an equivalent <em>user interface component</em>
+						which serves the same purpose and does meet the contrast requirements.</p>
+				</div>
+
 				</section>
 				<section>
 				<h4>Gradients</h4>