Merge pull request #2305 from w3c/feature/rs-conformance

Add reading system conformance section

epub33/rs/index.html

@@ -219,6 +219,29 @@ <h4>Relationship to SVG</h4>
 				</section>
 			</section>
 		</section>
+		<section id="sec-rs-conformance">
+			<h3>Reading system conformance</h3>
+
+			<p>Whether a reading system has to support a feature is mentioned at the beginning of its section. To be
+				conformant with this specification, reading systems MUST support all required features as well as all
+				applicable conditionally-required features (e.g., to support image rendering if the reading system has a
+				[=viewport=]) as defined in their respective sections.</p>
+
+			<p>When supporting recommended and optional features, reading systems MUST meet all normative requirements
+				as defined in their respective sections.</p>
+
+			<p>When reading system developers opt not to support a recommended or optional feature, it does not always
+				mean none of the normative requirements of the section apply. In some cases, there may be alternative
+				requirements when not implementing a feature (e.g., to <a href="#confreq-rs-scripted-flbk">process
+					fallbacks</a> when scripting is not supported). Reading systems MUST meet these alternative
+				requirements when not supporting a feature.</p>
+
+			<div class="note">
+				<p>EPUB publications frequently contain information not required by this specification (e.g., [=package
+					document=] metadata). Reading systems may use this additional information for any purposes (e.g., to
+					improve the user interface).</p>
+			</div>
+		</section>
 		<section id="sec-pub-resources">
 			<h3>Publication resource processing</h3>
 
@@ -2541,6 +2564,8 @@ <h2>Change log</h2>
 					>Working Group's issue tracker</a>.</p>
 
 			<ul>
+				<li>27-May-2022: Added reading system conformance section. See <a
+						href="https://github.com/w3c/epub-specs/issues/2271">issue 2271</a>.</li>
 				<li>27-May-2022: Added recommendation to only load remote resources referenced via https. See <a
 						href="https://github.com/w3c/epub-specs/issues/2263">issue 2263</a>.</li>
 				<li>20-May-2022: Removed the recommendation to prevent access to persistent storage from "unrelated