@ISSPACE[string]: Returns 1 if string is entirely composed of white space characters (0x09 - 0x0D or 0x20); 0 otherwise.
See also: @ISALNUM, @ISALPHA, @ISASCII, @ISCNTRL, @ISDIGIT, @ISPRINT, @ISPUNCT, @ISXDIGIT.
Example:
echo %@isspace[ ]
1
echo %@isspace[hello world]
0