Represents the "V" entry of the form field additional-actions dictionary object.

It is an optional entry defined as part of the PDF 1.3 specification.

It contains a JavaScriptActionElement.

For definitive details see:.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 196, page 416.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 199, page 505.

The validate action fires when the field loses focus after a value change and checks whether the new value satisfies constraints.