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+    <p>
+      For programmatic checking of modern HTML documents, you probably want
+      to instead use the API provided by the
+      <a href="https://validator.w3.org/nu/">W3C HTML Checker</a>. To do
+      that, call
+      <a href="https://validator.w3.org/nu/">https://validator.w3.org/nu/</a>
+      or the URL for another instance of the W3C HTML Checker, and consult
+      the following documentation:
+    </p>
+
+    <img src="/images/HTML5_Badge_128.png" alt="HTML5" class="html5_logo_128">
+    <ul>
+      <li><a href="https://github.com/validator/validator/wiki/Service:-Input:-GET">W3C HTML Checker GET interface</a></li>
+      <li><a href="https://github.com/validator/validator/wiki/Service:-Input:-POST-body">W3C HTML Checker POST interface</a></li>
+      <li><a href="https://github.com/validator/validator/wiki/Service:-Common-parameters">W3C HTML Checker parameters</a></li>
+      <li><a href="https://github.com/validator/validator/wiki/Output%3A-JSON">W3C HTML Checker out=json format</a></li>
+      <li><a href="https://github.com/validator/validator/wiki/Output:-XML">W3C HTML Checker out=xml format</a></li>
+      <li><a href="https://github.com/validator/validator/wiki/Output:-GNU">W3C HTML Checker out=gnu format</a></li>
+    </ul>
+    <p>
+      If for some reason rather than using the W3C HTML Checker API, you
+      want to use the W3C Markup Validator API, the simplest way to
+      do that is just to call <code>https://validator.w3.org/check?</code>
+      with a query string that includes the "<code>uri</code>" parameter
+      and the URL for the document to check, and with the
+      "<code>output=json</code>" parameter appended; for example:
+      <a href="https://validator.w3.org/check?uri=https://example.com/&amp;output=json">https://validator.w3.org/check?uri=https://example.com/&amp;output=json</a>.
+      The W3C Markup Validator will return the results as JSON, in
+      <a href="https://github.com/validator/validator/wiki/Output:-JSON">the same JSON format used by the W3C HTML Checker</a>.
+      You can specify other W3C Markup Validator options as additional query
+      parameters. The names of the query parameters are listed in the section
+      <a href="/docs/users.html#Options">Controlling the behavior of the W3C Markup Validator</a>,
+      in parentheses after the name of each option described.
+      All values for query parameters should be encoded in UTF-8 (before
+      percent-encoding them).
+      Separate the query parameters with either "<code>;</code>"
+      (semicolon) characters or with "<code>&amp;</code>" (ampersand)
+      characters.
+    </p>