in reply to
Re^2: Matching or masking specific characters in an array of strings
in thread Matching or masking specific characters in an array of strings
They're not talking about "masking away" characters from a given character set in a single string.
They're talking about masking multiple strings together in order find out which characters those strings have in common.
(where - (minus) is the masking operation.)
I reckon we are the only monastery ever to have a dungeon stuffed with 16,000 zombies.