@ISALNUM[string]: Returns 1 if string is entirely composed of alphabetic (a-z, A-Z) and/or numeric (0 - 9) characters; 0 otherwise.
See also: @ISALPHA, @ISASCII, @ISCNTRL, @ISDIGIT, @ISPRINT, @ISPUNCT, @ISSPACE, @ISXDIGIT.
Examples:
echo %@isalnum[123abc]
1
echo %@isalnum[123 abc]
0
echo %@isalnum[123.456]
0