Clarify the limitations of REQ 19C.

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@@ -223,7 +223,7 @@ <h2>General Guidance on Implementing Accessibility Features of Collaborative Env
         <li><em>REQ 19B:</em> Support the accessibility-related features of the user's operating system, user agent, and assistive technology. For example, some assistive technologies, such as screen readers, have features designed specifically for reading comments and suggested changes in textual content, which should be supported instead of defining application-specific functionality or keyboard commands that achieve the same purpose.</li>
         <li><em>REQ 19C:</em>Make collaborative features available via an <abbr title="application programming interface">API</abbr> to allow interoperability with tools with which the user may be familiar, and which may better satisfy a person's specific accessibility-related needs. For example, a revision control system could interoperate via an <abbr>API</abbr> with a user's chosen text editor or integrated development environment.</li>
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-      <p class="note">Provision of an <abbr>API</abbr> does not diminish the importance of ensuring that user interfaces provided by the application satisfy accessibility requirements.</p>
+      <p class="note">Provision of an <abbr>API</abbr> does not diminish the importance of ensuring that user interfaces provided by the application satisfy accessibility requirements. Nor is REQ 19C applicable to all collaborative environments. For example, some applications are highly dependent on editing functions specific to the tool itself, and should not be expected to interoperate with external editors.</p>
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