For Custom Validation list in BSK Gravity Forms Blacklist and Custom Validation we have the following rules for you to add to a list. You may choose one or multiple rules to do your validation.
Under the below form we the following rules:
DOB field, requires age at least 18 years old.
Address - Zip field, only start with 44
Mobile phone filed, only start with 1, length must be 10, must be number
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