The ISALPHA() and ISALPHANUM built-in functions return true if
the value of parameter 1 is all letters A-Z or a-z when ISALPHA is
used, or all letters or numbers when ISALPHNUM is used.
The ISCHAR() built-in function is similar to ISALPHANUM() but also permits blanks to be contained in the value for a positive result.
The ISNUM() checks for valid number and numeric edit symbols, including, period, comma, minus.
The ISDIGITS() checks for all digits.
The ISBLANK checks if the field is blank or empty The synonym ISEMPTY() may also be used.
#default &HouseAddr = '36w268 Silver Glen Rd';
// The address is valid.
// The address contains invalid data.
The House Address is assigned a value. In this example it is hard coded, but in real life it would probably be entered by the end-user or retrieved from a Session Variable or Database table.