The following issues are reported regarding headings in documentation comments.
For a general background information, see this message to jdk-dev@ojn.
   https://mail.openjdk.java.net/pipermail/jdk-dev/2019-March/002671.html

The headings are all in java.base, and I believe that in all cases will be reviewed by the core-libs team. Therefore I have not split this list into different bugs for different packages, unless people would prefer it that way.



open/src/java.base/share/classes/java/io/File.java:131: Note: missing heading <h2>
 * <h3>Interoperability with {@code java.nio.file} package</h3>
   ^
open/src/java.base/share/classes/java/io/DataInput.java:51: Note: missing heading <h2>
 * <h3><a id="modified-utf-8">Modified UTF-8</a></h3>
   ^
open/src/java.base/share/classes/java/time/Instant.java:111: Note: missing heading <h2>
 * <h3>Time-scale</h3>
   ^
open/src/java.base/share/classes/java/time/chrono/ChronoLocalDate.java:102: Note: missing heading <h2>
 * <h3>When to use this interface</h3>
   ^
open/src/java.base/share/classes/java/time/chrono/Chronology.java:136: Note: missing heading <h2>
 * <h3 id="addcalendars">Adding New Calendars</h3>
   ^
open/src/java.base/share/classes/java/time/chrono/ChronoZonedDateTime.java:106: Note: missing heading <h2>
 * <h3>When to use this interface</h3>
   ^
open/src/java.base/share/classes/java/time/chrono/ChronoLocalDateImpl.java:124: Note: missing heading <h2>
 * <h3>Adding Calendars</h3>
   ^
open/src/java.base/share/classes/java/time/chrono/ChronoLocalDateTime.java:105: Note: missing heading <h2>
 * <h3>When to use this interface</h3>
   ^
open/src/java.base/share/classes/java/time/temporal/WeekFields.java:123: Note: missing heading <h2>
 * <h3>Week of Month</h3>
   ^
open/src/java.base/share/classes/java/time/temporal/JulianFields.java:118: Note: low heading <h3>
     * <h3>Astronomical and Scientific Notes</h3>
       ^
open/src/java.base/share/classes/java/time/temporal/JulianFields.java:172: Note: low heading <h3>
     * <h3>Astronomical and Scientific Notes</h3>
       ^
open/src/java.base/share/classes/java/time/temporal/Temporal.java:95: Note: missing heading <h2>
 * <h3>When to implement</h3>
   ^
open/src/java.base/share/classes/java/time/temporal/IsoFields.java:94: Note: missing heading <h2>
 * <h3>Quarter of year</h3>
   ^
open/src/java.base/share/classes/java/time/ZoneId.java:114: Note: missing heading <h2>
 * <h3>Time-zone IDs</h3>
   ^
open/src/java.base/share/classes/java/time/format/DateTimeFormatter.java:153: Note: missing heading <h2>
 * <h3 id="predefined">Predefined Formatters</h3>
   ^
open/src/java.base/share/classes/java/lang/reflect/Proxy.java:159: Note: missing heading <h2>
 * <h3><a id="membership">Package and Module Membership of Proxy Class</a></h3>
   ^
open/src/java.base/share/classes/java/lang/ClassLoader.java:129: Note: missing heading <h2>
 * <h3> <a id="builtinLoaders">Run-time Built-in Class Loaders</a></h3>
   ^
open/src/java.base/share/classes/java/lang/ModuleLayer.java:123: Note: missing heading <h2>
 * <h3> Example usage: </h3>
   ^
open/src/java.base/share/classes/java/lang/invoke/VarHandle.java:237: Note: low heading <h1>
 * <h1>Compiling invocation of access mode methods</h1>
   ^
open/src/java.base/share/classes/java/lang/invoke/VarHandle.java:269: Note: low heading <h1>
 * <h1><a id="invoke">Performing invocation of access mode methods</a></h1>
   ^
open/src/java.base/share/classes/java/lang/invoke/VarHandle.java:332: Note: low heading <h1>
 * <h1>Invocation checking</h1>
   ^
open/src/java.base/share/classes/java/lang/invoke/VarHandle.java:367: Note: low heading <h1>
 * <h1>VarHandle creation</h1>
   ^
open/src/java.base/share/classes/java/lang/invoke/VarHandle.java:386: Note: low heading <h1>
 * <h1>Interoperation between VarHandles and the Core Reflection API</h1>
   ^
open/src/java.base/share/classes/java/lang/invoke/VarHandle.java:431: Note: low heading <h1>
 * <h1>Interoperation between VarHandles and Java generics</h1>
   ^
open/src/java.base/share/classes/java/lang/invoke/MethodHandles.java:271: Note: low heading <h1>
     * <h1><a id="lookups"></a>Lookup Factory Methods</h1>
       ^
open/src/java.base/share/classes/java/lang/invoke/MethodHandles.java:398: Note: low heading <h1>
     * <h1><a id="access"></a>Access checking</h1>
       ^
open/src/java.base/share/classes/java/lang/invoke/MethodHandles.java:532: Note: low heading <h1>
     * <h1><a id="secmgr"></a>Security manager interactions</h1>
       ^
open/src/java.base/share/classes/java/lang/invoke/MethodHandles.java:591: Note: low heading <h1>
     * <h1><a id="callsens"></a>Caller sensitive methods</h1>
       ^
open/src/java.base/share/classes/java/lang/invoke/MutableCallSite.java:200: Note: low heading <h1>
     * <h1>Java Memory Model details</h1>
       ^
open/src/java.base/share/classes/java/lang/invoke/MethodHandle.java:55: Note: low heading <h1>
 * <h1>Method handle contents</h1>
   ^
open/src/java.base/share/classes/java/lang/invoke/MethodHandle.java:92: Note: low heading <h1>
 * <h1>Method handle compilation</h1>
   ^
open/src/java.base/share/classes/java/lang/invoke/MethodHandle.java:124: Note: low heading <h1>
 * <h1>Method handle invocation</h1>
   ^
open/src/java.base/share/classes/java/lang/invoke/MethodHandle.java:167: Note: low heading <h1>
 * <h1>Invocation checking</h1>
   ^
open/src/java.base/share/classes/java/lang/invoke/MethodHandle.java:208: Note: low heading <h1>
 * <h1>Method handle creation</h1>
   ^
open/src/java.base/share/classes/java/lang/invoke/MethodHandle.java:266: Note: low heading <h1>
 * <h1>Usage examples</h1>
   ^
open/src/java.base/share/classes/java/lang/invoke/MethodHandle.java:312: Note: low heading <h1>
 * <h1>Exceptions</h1>
   ^
open/src/java.base/share/classes/java/lang/invoke/MethodHandle.java:325: Note: low heading <h1>
 * <h1><a id="sigpoly"></a>Signature polymorphism</h1>
   ^
open/src/java.base/share/classes/java/lang/invoke/MethodHandle.java:350: Note: low heading <h1>
 * <h1>Interoperation between method handles and the Core Reflection API</h1>
   ^
open/src/java.base/share/classes/java/lang/invoke/MethodHandle.java:392: Note: low heading <h1>
 * <h1>Interoperation between method handles and Java generics</h1>
   ^
open/src/java.base/share/classes/java/lang/invoke/MethodHandle.java:419: Note: low heading <h1>
 * <h1><a id="maxarity"></a>Arity limits</h1>
   ^
open/src/java.base/share/classes/java/lang/invoke/MethodHandleInfo.java:38: Note: low heading <h1>
 * <h1><a id="directmh"></a>Direct Method Handles</h1>
   ^
open/src/java.base/share/classes/java/lang/invoke/MethodHandleInfo.java:61: Note: low heading <h1>
 * <h1>Restrictions on Cracking</h1>
   ^
open/src/java.base/share/classes/java/lang/invoke/MethodHandleInfo.java:80: Note: low heading <h1>
 * <h1><a id="refkinds"></a>Reference kinds</h1>
   ^
open/src/java.base/share/classes/java/lang/Character.java:47: Note: missing heading <h2>
 * <h3><a id="conformance">Unicode Conformance</a></h3>
   ^
open/src/java.base/share/classes/java/lang/module/Configuration.java:78: Note: missing heading <h2>
 * <h3> Example </h3>
   ^
open/src/java.base/share/classes/java/text/Format.java:61: Note: missing heading <h2>
 * <h3>Subclassing</h3>
   ^
open/src/java.base/share/classes/java/text/ChoiceFormat.java:154: Note: missing heading <h2>
 * <h3><a id="synchronization">Synchronization</a></h3>
   ^
open/src/java.base/share/classes/java/text/NumberFormat.java:178: Note: missing heading <h2>
 * <h3><a id="synchronization">Synchronization</a></h3>
   ^
open/src/java.base/share/classes/java/text/SimpleDateFormat.java:77: Note: missing heading <h2>
 * <h3>Date and Time Patterns</h3>
   ^
open/src/java.base/share/classes/java/text/DateFormat.java:143: Note: missing heading <h2>
 * <h3><a id="synchronization">Synchronization</a></h3>
   ^
open/src/java.base/share/classes/java/text/MessageFormat.java:71: Note: missing heading <h2>
 * <h3><a id="patterns">Patterns and Their Interpretation</a></h3>
   ^
open/src/java.base/share/classes/java/text/DecimalFormat.java:87: Note: missing heading <h2>
 * <h3>Patterns</h3>
   ^
open/src/java.base/share/classes/java/text/CompactNumberFormat.java:76: Note: missing heading <h2>
 * <h3><a id="compact_number_style">Style</a></h3>
   ^
open/src/java.base/share/classes/java/net/Inet4Address.java:39: Note: missing heading <h2>
 * <h3> <a id="format">Textual representation of IP addresses</a> </h3>
   ^
open/src/java.base/share/classes/java/net/Inet6Address.java:41: Note: missing heading <h2>
 * <h3> <a id="format">Textual representation of IP addresses</a> </h3>
   ^
open/src/java.base/share/classes/java/net/URI.java:67: Note: missing heading <h2>
 * <h3> URI syntax and components </h3>
   ^
open/src/java.base/share/classes/java/net/InetAddress.java:74: Note: missing heading <h2>
 * <h3> Address types </h3>
   ^
open/src/java.base/share/classes/java/util/spi/LocaleServiceProvider.java:45: Note: missing heading <h2>
 * <h3>Packaging of Locale Sensitive Service Provider Implementations</h3>
   ^
open/src/java.base/share/classes/java/util/spi/ResourceBundleProvider.java:38: Note: missing heading <h2>
 * <h3>Developing resource bundle services</h3>
   ^
open/src/java.base/share/classes/java/util/TimeZone.java:117: Note: missing heading <h2>
 * <h3>Three-letter time zone IDs</h3>
   ^
open/src/java.base/share/classes/java/util/GregorianCalendar.java:94: Note: missing heading <h2>
 * <h3><a id="week_and_year">Week Of Year and Week Year</a></h3>
   ^
open/src/java.base/share/classes/java/util/regex/Pattern.java:80: Note: missing heading <h2>
 * <h3><a id="sum">Summary of regular-expression constructs</a></h3>
   ^
open/src/java.base/share/classes/java/util/Scanner.java:158: Note: missing heading <h2>
 * <h3> <a id="localized-numbers">Localized numbers</a> </h3>
   ^
open/src/java.base/share/classes/java/util/Calendar.java:100: Note: missing heading <h2>
 * <h3>Getting and Setting Calendar Field Values</h3>
   ^
open/src/java.base/share/classes/java/util/ServiceLoader.java:72: Note: missing heading <h2>
 * <h3> Obtaining a service loader </h3>
   ^
open/src/java.base/share/classes/java/util/ResourceBundle.java:207: Note: missing heading <h2>
 * <h3><a id="resource-bundle-modules">Resource Bundles and Named Modules</a></h3>
   ^
open/src/java.base/share/classes/java/util/Formatter.java:143: Note: missing heading <h2>
 * <h3><a id="org">Organization</a></h3>
   ^
open/src/java.base/share/classes/java/util/Locale.java:193: Note: missing heading <h2>
 * <h3><a id="def_locale_extension">Unicode locale/language extension</a></h3>
   ^
open/src/java.base/share/classes/java/lang/invoke/package-info.java:56: Note: low heading <h1>
 * <h1><a id="jvm_mods"></a>Dynamic resolution of call sites and constants</h1>
   ^
open/src/java.base/share/classes/java/lang/module/package-info.java:37: Note: low heading <h1>
 * <h1><a id="resolution"></a>{@index "Module Resolution"}</h1>
   ^