Returns .true if the character at position n matches any character of the string chars. Returns .false if the character does not match any of the characters in the reference set. The match is made using caseless comparisons. The argument n must be a positive whole number.

"a+b"~caselessMatchChar(2, "+-*/")           -->    1
"a+b"~caselessMatchChar(1, "+-*/")           -->    0
"Friday"~caselessMatchChar(3, "aeiou")       -->    1
"FRIDAY"~caselessMatchChar(3, "aeiou")       -->    1