When etc. is at the end of a sentence, do you add an extra period to denote the sentence ending?
But a compiler will accept ;; as a statement ending - which is the C type programs period - they simply strip off anything on that line after the ;.
Of course, there could be programs that would.
Who knows, maybe some human writing systems allow it as well.
I think BLISS may (System Software Implementation Language Backwards, ho-ho). But I never saw any, let alone wrote it.