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 or brand guidelines. However, this can be problematic when
+            logos or logotypes act as <a>user interface components</a> (such as a link or
+            other interactive control). In these cases, as a best practice, choose a variant of
+            the logo or logotype that has sufficient text contrast, if allowed by the
+            corporate identity or brand guidelines. Alternatively, consider providing equivalent
+            <a>user interface components</a> which serve the same purpose and meet
+            the contrast requirements.</p>
+      </div>
+
       <section>
 
          <h3>Rationale for the Ratios Chosen</h3>

understanding/20/contrast-minimum.html

@@ -94,7 +94,7 @@ <h2>Intent of Contrast (Minimum)</h2>
          a street sign, are not included. Nor is text that for some reason is designed to be
          invisible to all viewers. Stylized text, such as in corporate logos, should be treated
          in terms of its function on the page, which may or may not warrant including the content
-         in the text alternative. Corporate visual guidelines beyond logo and logotype are
+         in the text alternative. Corporate identity or brand guidelines beyond logo and logotype are
          not included in the exception.
       </p>
 
@@ -127,6 +127,18 @@ <h2>Intent of Contrast (Minimum)</h2>
          <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 or brand guidelines. However, this can be problematic when
+            logos or logotypes act as <a>user interface components</a> (such as a link or
+            other interactive control). In these cases, as a best practice, choose a variant of
+            the logo or logotype that has sufficient text contrast, if allowed by the
+            corporate identity or brand guidelines. Alternatively, consider providing equivalent
+            <a>user interface components</a> which serve the same purpose and meet
+            the contrast requirements.</p>
+      </div>
+
       <section>
          <h3>Rationale for the Ratios Chosen</h3>
 

understanding/21/non-text-contrast.html

@@ -401,6 +401,29 @@ <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>
+
+				<h4>Logos</h4>
+
+				<p>Logos 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 or brand guidelines. When they act as <a>user interface components</a>
+				(such as links or other interactive controls), authors must nonetheless make sure that there is an aspect of
+				the user interface components that allows users to identify the components.
+				If possible, and if allowed by the relevant corporate identity or brand guidelines, authors should choose a
+				variant of the logo that has sufficient contrast. Alternatively, authors should provide an additional
+				visual element with sufficient contrast that helps identify the user interface component  – such as
+				additional text, or an outline or border around the component. Lastly, consider providing an equivalent
+				<a>user interface component</a> which serves the same purpose and does meet the contrast requirements.</p>
+
+				<p>If logos are presented with insufficient contrast, but their presentation was an author choice rather than
+				being mandated by corporate identity or brand guidelines, then that particular low contrast presentation is
+				<em>not</em> "essential", and the logo is <em>not</em> exempt from the contrast requirements.</p>
+
+				<figure id="figure-low-contrast-logos-author-choice">
+					<img src="img/1.4.11-ntc-author-choice-logos.png" alt="A heading: 'ACME tool is trusted by the world's most innovative companies.'; below the heading, a series of nine company logos, all presented as very dark grey logos on the page's black background, with very low contrast; one logo is hovered with the mouse, and is displayed in white, with high contrast against the page background.">
+				<figcaption>An author chooses to present company logos with low contrast by default, until they are hovered; the fact that these are logos doesn't exempt this scenario from failing the requirements of this success criterion, as the initial low contrast presentation is not "essential"</figcaption>
+				</figure>
+
 				</section>
 				<section>
 				<h4>Gradients</h4>
@@ -453,7 +476,9 @@ <h4>Essential Exception</h4>
 
 					<p>Graphical objects do not have to meet the contrast requirements when &quot;a particular presentation of graphics is essential to the information being conveyed&quot;. The Essential exception is intended to apply when there is no way of presenting the graphic with sufficient contrast without undermining the meaning. For example:</p>
 					<ul>
-						<li><strong>Logotypes and flags</strong>: The brand logo of an organization or product is the representation of that organization and therefore exempt. Flags may not be identifiable if the colors are changed to have sufficient contrast.</li>
+						<li><strong>Logotypes</strong>: The brand logo of an organization or product is the representation of that organization, and is often
+							presented in the brand's specific colors; it is therefore exempt.</li>
+						<li><strong>Flags</strong>: Flags may not be identifiable if the colors are changed to have sufficient contrast.</li>
 						<li><strong>Sensory</strong>: There is no requirement to change pictures of real life scenes such as photos of people or scenery.</li>
 						<li><strong>Representing other things</strong>: If you cannot represent the graphic in any other way, it is essential. Examples include:
 							<ul>