|1|| Input is non-numeric.|
|0|| Input is numeric.|
|StringValue||String value to check.|
Determines whether value is non-numeric by checking if it is empty or it is not an integer, double, wide integer, or entier. Roughly speaking, if IsNonNumeric returns true then probably would not be able to use that value with expr, though there are exceptions (see documentation for expr).
For information regarding exceptions / errors, see here
% IsNonNumeric asdf
% IsNonNumeric 123