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First Let us understand What are Jira Expressions and its features.
Adding Expressions to Workflows:
You Users can add expressions in the Workflow transitions using Expression pluginExpressions for Jira App.Expression Repository:
To manage your the workflows which that are using Expressions for Jira, visit the Expression Expressions repository in the Manage Apps page.Expressions Custom Field:
Users can calculate the custom field values using Jira Expressions.RegEx Custom Field:
Regular Expression enables users to validate a custom field.
Next page Configure Expressions