A picture validation function may be specified for the new field type. A picture validation function is not required but if one is specified it will be used to check the validity of the picture specified for the field in fld_def(). Picture validation functions are a feature to aid you in developing application programs, by letting you know if you have specified an invalid picture for a field. They are only called in the development version of the Vermont Views libraries.
The picture validation function provided by the system, pic_val() and #defined as PICVALFP, is generic enough to use for most new field types. Function pic_val() makes sure that any picture control characters in the picture are allowed for the field type, that there is at least one picture control character in the picture, and that all picture flags as specified in the field type structure are respected.
You will have to write your own picture validation function only if (1) you want to incorporate picture validation for the field type and (2) if there are requirements that are not addressed by the available picture flags. You can always call pic_val() in your picture validation function and do additional processing.
Specifications for Picture Validation Functions
Referring to Picture Control Characters
