Validation functions are designed to control the values of the data entered in a field by the user and have different requirements than form, field, and event functions. We recommend using validation functions for checking and validating the user's entry and reserving end-field functions for changing the flow of form processing.
Validation functions can be installed for the form or any field. Form validation functions are useful for doing cross-field validations.
See Chapter 32, "Writing User Validation Functions," for more information about using and writing field and form validation functions.
