In the Options menu is an option, Multiple Regions, which affects how Trim, Extend and Clip functions work. For example, with Multiple Regions off, a clipped geometry might be considered as multiple separate lines. Turning on Multiple Regions, the clipped geometry is considered one line, even though it displays in multiple segments. Selecting either segment selects the entire line, or both segments. Trim and extend can extend separate segments, or extend visible portions of lines depending on the setting of Multiple Regions.