The following four features have been removed from the _javadoc_ tool:
_Support for generating API documentation using HTML 4:_ Support for HTML 5 was added in JDK 9 and has been the default since JDK 11. To generate API documentation that is fully compliant with the HTML 5 specification, developers should ensure that any use of HTML tags in their documentation comments is also compliant with the HTML 5 specification.
_Support for the "old" javadoc API:_ This includes the API (`com.sun.javadoc`), the old standard doclet (`com.sun.tools.doclets.standard`), and the old entry point (`com.sun.tools.javadoc.Start`), all in the `jdk.javadoc` module. A new API and a new standard doclet were introduced in JDK 9, leveraging other modern modeling API such as `javax.lang.model`. The _javadoc_ tool can be programmatically invoked using the `javax.tools.DocumentationTool` API, or (for simple use) `java.util.spi.ToolProvider`. Users that just use the _javadoc_ tool to generate standard API documentation are not affected.
_Support for generating documentation using HTML frames:_ It has been replaced by the "Search" feature, added in JDK 9, and by improved index files and links within pages.
_Support for the `--no-module-directories` option:_ This option provided limited support for the organization used for the generated documentation by the _javadoc_ tool in JDK 9 and 10, in which the files for different modules were not grouped into separate directories.