What is a "validator" in a JIRA workflow, and how does it work?

A "validator" in a JIRA workflow is a rule or condition that must be satisfied before a transition can be executed. Validators are used to enforce specific requirements or checks on an issue before it moves from one status to another. For example, you can use a validator to ensure that certain fields are filled out, or that certain conditions are met before an issue can be transitioned to a different workflow status. Validators help maintain data integrity and enforce workflow rules.