Just to confirm, does this/should this match something like java.base/arrays.helpers/Collection (or some other example where / appears twice)? Is that even valid? If it's invalid should we still highlight it? Does it matter (maybe not)? Thoughts?

Good questions. I investigated a little: The print method of Java Throwable uses the standard toString method of StackFrameElement which is technically implementation-defined but the doc lists some examples of what you can expect. Examples like com.foo.loader/foo@9.0/com.foo.Main.run(Main.java:101), com.foo.loader/foo@9.0/com.foo.Main.run(Unknown Source), and acme@2.1/org.acme.Lib.test(Lib.java:80).

Why can't it ever be easy...

I'll fix it.

Also, I intentionally made the stack frame pattern more accepting than it has to be. This makes the pattern simpler and more robust in case I forgot a case (like I did).