We need to investigate and (probably) improve the documentation for arg files on the javac and javadoc tools reference guides.

See mail thread beginning here:
https://mail.openjdk.java.net/pipermail/javadoc-dev/2018-December/000778.html

And continued here:
https://mail.openjdk.java.net/pipermail/javadoc-dev/2019-January/000779.html

There's a good write up here, for the "java" launcher
https://docs.oracle.com/en/java/javase/11/tools/java.html#GUID-4856361B-8BFD-4964-AE84-121F5F6CF111
The spec for the content for javac and javadoc is the same, but there is a slight difference with respect to the file encoding used by javac/javadoc, compared to the encoding expected by java.