Verify Methods
These methods are used in VERIFY clauses. In practice, Verify Methods are used for two purposes: verifying checksums and CRCs, and validating the values in fields. We will examine Verify Methods broken down into these two groups. In principle, Verify Methods could also be applied to other kinds of internal consistency checks, for example verifying that two length fields are consistent.
A verify function returns True or False; when False is returned then the field is displayed in red in the decode and text explaining the error is appended to the method's output string.
As with Retrieve methods, you can string together multiple Verify methods using the keyword ALSO.