Box is a Control that holds a group of Controls horizontally or vertically. If horizontally, then all controls have the same height. If vertically, then all controls have the same width. By default, each control has its preferred width (horizontal) or height (vertical); if a control is marked "stretchy", it will take whatever space is left over. If multiple controls are marked stretchy, they will be given equal shares of the leftover space. There can also be space between each control ("padding").

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