@ISASCII[string]: Returns 1 if string is entirely composed of 7-bit ASCII characters (0x00 - 0x7F); 0 otherwise.
See also: @ISALNUM, @ISALPHA, @ISCNTRL, @ISDIGIT, @ISPRINT, @ISPUNCT, @ISSPACE, @ISXDIGIT.
Examples:
echo %@isascii[abc]
1
echo %@isascii[abc 123]
1
echo %@isascii["abc"a]
0