ISSTRING
b = ISSTRING (x)
Returns true if x is a string and cannot be converted to a number.
Example
print ISSTRING(12) ' Output 0
print ISSTRING("12") ' Output 0
print ISSTRING("12E+2") ' Output 0
print ISSTRING("abc") ' Output 1
print ISSTRING("1+2") ' Output 1
print ISSTRING("int(2.4)") ' Output 1