Forms for Confluence provides access to velocity to capture logged in users information and adds this as the value for the field. This is particularly useful when you want to make forms simple and quick to fill out. We've limited the values you can obtain from velocity for security reasons, however you can obtain velocity values using the following calls in the Velocity Value field:
$queryparam= allows the user to specify a parameter that will be present in the url so that it can be fetched by the Hidden Field Macro. This is specially useful when sharing surveys with anonymous customers and one wants to capture for example the email address.