Example:

source code - jdk/src/java.base/share/classes/javax/security/auth/Policy.java

...
 * @deprecated as of JDK version 1.4 -- Replaced by java.security.Policy.
 * java.security.Policy has a method:
 * <pre>
 * public PermissionCollection getPermissions
 * (java.security.ProtectionDomain pd)
 *
 * </pre>
 * and ProtectionDomain has a constructor:
 * <pre>
 * public ProtectionDomain
 * (CodeSource cs,
 * PermissionCollection permissions,
 * ClassLoader loader,
 * Principal[] principals)
 * </pre>
 *
 * These two APIs provide callers the means to query the
 * Policy for Principal-based Permission entries.
 *
 * @see java.security.Security security properties
 */
@Deprecated
public abstract class Policy {
...

generated html - build/linux-x86_64-normal-server-release/images/docs/api/javax/security/auth/Policy.html

...
<div class="block"><span class="deprecatedLabel">Deprecated.</span>&nbsp;
<div class="block"><span class="deprecationComment">as of JDK version 1.4 -- Replaced by java.security.Policy.
              java.security.Policy has a method:
 <pre>
      public PermissionCollection getPermissions
          (java.security.ProtectionDomain pd)

 </pre>
 and ProtectionDomain has a constructor:
 <pre>
      public ProtectionDomain
          (CodeSource cs,
           PermissionCollection permissions,
           ClassLoader loader,
           Principal[] principals)
 </pre>

 These two APIs provide callers the means to query the
 Policy for Principal-based Permission entries.</span></div>
</div>
...

So the <span> tag contains nested <pre> causing warnings:

tidy -e Policy.html

line 120 column 20 - Warning: missing </span> before <pre>
line 128 column 2 - Warning: inserting implicit <span>
line 128 column 2 - Warning: missing </span> before <pre>
line 137 column 2 - Warning: inserting implicit <span>