Venting adds copper which isn't connected to any nets on the board and does not affect the functionality. The are various purposes for Venting (i.e Thieving) such as improving etching throughout the entire panel, to improve manufacturing efficiency, and more. Typically small copper circles, squares or even a solid copper plane will be added to larger blank spaces to even out the copper distribution across a copper layer.
Rail: Uniform metal places around the perimeter of the panel.
VRail: Add Vertical Rails only.
HRail: Add Horizontal Rails only.
Solid: Add solid copper to available areas/layers.
Dot: Add dot patterns to available copper areas/layers.
Hatch: Add hatched patterns to available copper areas/layers.
Each pattern has different requirements. Typically only Dot and Hatch make use the Pattern descriptions, and must be comma separated.
Rail: Overall width of rail (around all 4 sides)
VRail: Width of vertical rail (2 sides)
HRail: Height of vertical rail (2 sides)
Clearance from Panel extents.
Clearance from inserted jobs in the panel.
Clearance from external resources like coupons.
Note: FAB 3000 includes several sample Panel Setup files (*.pan) which make use of various venting patterns. We recommend trying those samples and evaluating the venting pattern results.