Upbars

An upbar or pick-up is a bar often found at the start of a tune (or part of it) having less duration than prescribed by the tune's meter.

An upbar is established by forcing preliminary end-of-bar by inserting a bar line using the bar line-menu or the shortcut <⎥>

A similar construct is possible whenever you need an incomplete bar in the middle of a tune (bar number 4).