Experienced contractors take a number of steps to keep this from happening. You'll also see a row of slots at the top of each panel. That allows each panel to move slightly with temperature changes. The detail shown here is tricky because the wall being sided adjoins the sloping roof of a garage. Here, a contractor trims a length of coated tin before applying it to a window.
Mitered corners are a sign of quality work.
The channel holds the edges of siding panels that abut the window, providing a clean, crisp finish to the end of a panel run. Because installation is so important, check references of any contractor you're considering. Request written estimates, then visit past jobs and a current project to give them a thorough once-over. It provides a smooth surface for the siding, adds some insulating value and cuts air infiltration. Joints between rigid insulation panels should be taped for maximum energy savings.