Included in Hair are several special Hair Nodes, whose primary purpose is the detection of position and collision of hair or guides (or other elements located thereon) with other objects.
You can select a Hair Node in the XPresso editor by right-clicking on the XGroup window and selecting one of the six available Hair Nodes in the New Node / Hair / General or Iterator menu.
In addition, even more precise results can be achieved within this sequence of priorities by assigning corresponding priorities outside of this sequence. A normal XPresso tag has an Expression 0 priority. In order to execute the Hair object prior to the XPresso tag being executed, its priority can, for example, be set to Animation or Expression 0 (the XPresso tag will then have to be set to Expression 1).