Edits to Challenge #3, including new mitigation paragraph.

conformance-challenges/index.html

@@ -103,13 +103,13 @@ <h2>Challenge #2: Large, complex, and dynamic websites may have too many changin
         </section>
 	<section id="Challenge-3">
             <h2>Challenge #3: 3rd party content</h2>
-            <p>Very large, highly dynamic web sites generally aggregate content provided by multiple entities. Many of these are third parties with the ability to add content directly to the website – including potentially every website visitor. While the website can provide guidance on how to post content so that it meets WCAG Guidelines and Success Criteria, it is ultimately up to those third parties to understand and correctly implement that guidance. And as noted above, even with automated checking prior to accepting the post, many Guidelines and Success Criteria expect human validation involvement.</p>
-            <p>Copyright and similar constraints that restrict the ability to modify or impose requirements on third party data can also make full page conformance impossible to assure. For instance: articles that allow reposting but without modification due to copyright restrictions.</p>
+            <p>Very large, highly dynamic web sites generally aggregate content provided by multiple entities. Many of these are third parties with the ability to add content directly to the website &mdash; including potentially every website visitor. While the website can provide guidance on how to post content so that it meets WCAG guidance, it is ultimately up to those third parties to understand and correctly implement that guidance. And as noted above, even with automated checking prior to accepting the post, many Guidelines and Success Criteria expect human validation involvement.</p>
+            <p>Copyright and similar constraints that restrict the ability to modify or impose requirements on third party data can also make full page conformance impossible to assure, e.g. articles that allow reposting but without modification due to copyright restrictions.</p>
 	    <section id="Challenge-3.1">
 <h3>Treatment of 3rd party content and Statements of Partial Conformance</h3>
 <p>WCAG 2.x speaks to 3rd party content and conformance, in the context of a 
 <a href="https://www.w3.org/TR/WCAG21/#conformance-partia">Statement of
-Partial Conformance</a>. [[wcag21]] It provides two options for such content&mdash;that
+Partial Conformance</a>. [[wcag21]] It provides two options for such content &mdash; that
 pages with 3rd party content may:
 <ol>
 	<li>Make a determination of conformance <q>based on best knowledge,</q> for example
@@ -127,6 +127,23 @@ <h3>Treatment of 3rd party content and Statements of Partial Conformance</h3>
 party content doesn't scale.</p>
 <p>A statement of partial conformance doesn't address the underlying challenge of improving the usability of 3rd party content.  While it might allow a web page/website visitor to be forewarned in advance that they should 
 anticipate encountering inaccessible content, it does little to practically enable large sites to address such concerns.</p>
+<p class="mitigation">There are several approaches to the challenge of 3rd party content
+accessibility.  Where that content is provided as part of a commercial
+contract, the terms of the contract may include requirements around
+accessibility.  Where the content comes from potentially any website visitor
+or user, those visitors can be constrained in the types of contributions they
+can make (e.g. prevented from using non-semantic text attributes like
+boldface), or prompted to add accessibility metadata (e.g. so that images are
+uploaded along with ALT text), or reminded about good accessibility practices
+(e.g. told not refer to sensory characteristics in their text).  Such
+approaches may add substantial friction, especially to individual website
+visitors and users, to the point that they may be disinclined to make
+contributions.  Further, they aren't a guarantee of perfection in those
+contributions (Is the ALT text thoughtfully authored, or just filler text to
+make the upload happen? Did the text truly avoid reference to sensory
+characteristics?).  Nonetheless, these are some approaches to consider to help
+minimize the amount of 3rd party content that poses accessibility challenges.
+</p>
 </section>
         </section>
         <section id="Challenge-4">