Rhythm lines handle ties between notes and can have joined tail notes too, but they aren't currently as "automatic" as ties and joins in staff lines.
To enter a symbol tie in a rhythm line click on the "short tie" button on the main symbols toolbox, or if the rhythm line is in "Symbol Entry" mode, hit the "n" key (only down-curved ties can be entered as symbols). To enter an "extended object" tie in a rhythm line, click where the tie will start, click on the Insert Down- (or Up-) curved tie, click where the midpoint of the tie arc should be, then click where the tie should end. (You can't select notes and hit the "Insert Tie" button to join them as you can in a staff line). After the tie appears you can click on it and adjust its position and shape as with other extended objects.
Joining (beaming) notes is also handled a bit differently in rhythm lines. To join notes put MusEdit in "Join Mode" by clicking on (or hit Ctrl+J), then enter joinable notes (8th, 16th, 32nd, or 64th). Joins cannot cross any intervening symbols, such as a rest, tie, dot, or even a space. If you want to space out joined notes, enter them close together so they are joined, then click between them and hit the space bar after they are joined. You can't join notes by selecting joinable notes and hitting the Join button the way you can in Staff lines.
Examples of ties and joined notes in a Rhythm line:
( TiesAndJoinsInRhythmLines.med )