See screenshot.

This occurred when adding an {@index javac} to the first sentence of the jdk.compiler module-info.java doc comment.

I'm also seeing repeated occurrences for other new uses of {@index}. Some give 2 occurrences, some give 3.

Here is the confirmation that there is only one instance in the code:

$ grep -r "index javac" langtools/src
langtools/src/jdk.compiler/share/classes/module-info.java: * and its command line equivalent, <em>{@index javac}</em>,