If the REPLACEMENTLIST is empty, the SEARCHLIST is replicated. This latter is useful for counting characters in a class
Furthermore, this used to effectively replace characters by themselves, causing it to fail on read-only values, but that has been fixed. Now tr/%// merely counts.

In reply to Re^3: Counting how many times a character is in a string. by bart
in thread Counting how many times a character is in a string. by slloyd

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