I'm looking at a pice of music that shows an arpeggio between two dotted half-notes in one voice and a quarter-note in the other voice. Specifically, in the wee snippet below, the first e4 in the first voice is at the top of the arpeggio above the <gs~ b>2 in the second voice.
%%%%%%%%%%%%%%%%%% << { e4 e4 b4 | % 1 e2 b8[ b8] | % 2 } \\ { <gs~ b>2.\arpeggio | % 1 \stemUp gs2 \stemNeutral s4 | % 2 } >> %%%%%%%%%%%%%%%%%%