For example, if a user wants to find occurrences of a particular word in a document, a main window will often open a dialog box to ask a user what word they are looking for.
Since finding a word doesn't prevent a user from editing the document, however, the dialog box doesn't need to be modal.
The rules may be implemented through the automated facilities of a data dictionary, or by the inclusion of explicit application program validation logic.
Data validation is intended to provide certain well-defined guarantees for fitness, accuracy, and consistency for any of various kinds of user input into an application or automated system.
Data validation rules may be defined, designed and deployed, for example: Definition and design contexts: Data that does not conform to these rules will negatively affect business process execution.
Therefore, data validation should start with business process definition and set of business rules within this process.
Rules can be collected through the requirements capture exercise.
Take a look at the SPF record syntax to get a better understanding of what your record means.
Go back to the validator and put the domain part of your e-mail address in the domain part of the second test and your draft record in the SPF record part (do enclose it in quotes, just the record) and then click on "Check SPF Record".