The doclet toolkit package is supposed to be format-neutral, yet there a few import dependencies on formats.html

$ grep -r formats.html src/jdk.javadoc/share/classes/jdk/javadoc/internal/doclets/toolkit/util
src/jdk.javadoc/share/classes/jdk/javadoc/internal/doclets/toolkit/util/ClassUseMapper.java:import jdk.javadoc.internal.doclets.formats.html.HtmlConfiguration;
src/jdk.javadoc/share/classes/jdk/javadoc/internal/doclets/toolkit/util/Utils.java:import jdk.javadoc.internal.doclets.formats.html.HtmlConfiguration;
src/jdk.javadoc/share/classes/jdk/javadoc/internal/doclets/toolkit/util/links/LinkFactory.java:import jdk.javadoc.internal.doclets.formats.html.LinkInfoImpl;