Which characters are not allowed in Java 9 module names?

Question

Dashes are not allowed in the JPMS module names. As I understand it is suggested to replace them with dots.

However I cannot find a list of other not allowed characters in Java modules names with replacement suggestions. For example, is "_" character allowed?

Answer 1

The Java Language Specification, section 7.7. Module Declarations, says:

A module name consists of one or more Java identifiers (§3.8) separated by "." tokens.

So the valid characters for a module name is the same as for the fully qualified name of a class.