xpText Object tab menu.
Checking this box activates xpText.
Set at Independent, by default.
You can change this to Action-Controlled.
In this mode, particles will be affected if they come into the field of effect of the modifier.
When in the Action-Controlled Mode setting, the modifier will only act on a particle when told to do so by an action.
When the modifier is using fields, the effect of the modifier is dependent on a particle’s position within the field.
Threshold is a user-designated point between the start of the field and the field's inner offset.