Typically, for hard plastic devices, this value is set to 2, meaning it is preceded by a second surface (MC2) cut. If set to 1, the top surface is written to, which is not really practical except on automatic tool change systems.
If this value is set to anything other value, engraving is disabled for this order.
Typically, textsurf is set to 2 for plastic, and 1 for positives and single sided accomodative devices.