X is a STRING scalar/vector.
Y is an integer scalar/vector. If Y is a vector, it must be of the same length as X.
Return the character in X at the position specified by Y. The result is a scalar/vector of data type CHAR.
$ s=charAt("abc",2); $ s; 'c' $ typestr(s); CHAR $ charAt(["hello","world"],[3,4]); ['l','d']