Task mode defines how parents behave. The task mode can be selected from task context menu.
Bottom-up mode In this mode parent length is calculated from children. Parent starts where the first child starts, and parent ends where the last child ends. As parent is defined by children, it's not possible to resize the parent itself in this mode. Moving a child will automatically change the length of the parent. For example, moving rightmost child one day to the right will automatically make the parent one day longer.
Manual mode In this mode parent length is independent from children. Parent can start before the first child starts, and parent can end after the last child ends.
In case the parent is resized or moved in such a way, that some child goes out of parent boundaries - a conflict will be highlighted for your information. In example below, a child starts one day before the parent starts. You can fix the conflict either by moving the child or by resizing the parent.
In case you decide to use modes other than bottom-up, add column Mode to the chart. It will show selected mode for each task. For example, below all tasks are in bottom-up mode (arrow), except for one task. The manual mode task shows a hand icon.