What is the "discourse" predicate trying to say?

If I parse “Hi Lexi!” I get this MRS:

[ LTOP: h0 INDEX: e2 [ e SF: prop ] 
RELS: < 
[ greet<0:2> LBL: h4 CARG: "hi" ARG0: i6 ]  
[ discourse<0:2> LBL: h1 ARG0: i7 ARG1: h4 ARG2: h8 ]  
[ unknown<3:8> LBL: h8 ARG0: e2 ARG: x9 [ x PERS: 3 NUM: sg IND: + ] ]  
[ proper_q<3:8> LBL: h10 ARG0: x9 RSTR: h11 BODY: h12 ]  
[ named<3:8> LBL: h13 CARG: "Lexi" ARG0: x9 ] > 
HCONS: < h0 qeq h1 h11 qeq h13 > ICONS: < > ]

The greet predicate is nice since it removes having to deal with all the greeting words separately.

However, it is unclear to me what the discourse predicate is trying to tell me. Since it is tying together “Hi” and “Lexi” I assume it is being used as a predicate that represents “a thing that is said at someone that doesn’t have any meaning other than chit chat”???