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A splitter (TSplitter) placed between aligned controls allows users to resize the controls. Used with components like panels and group boxes, splitters let you divide a form into several panes with multiple controls on each pane.
After placing a panel or other control on a form, add a splitter with the same alignment as the control. The last control should be client-aligned, so that it fills up the remaining space when the others are resized. For example, you can place a panel at the left edge of a form, set its Alignment to alLeft, then place a splitter (also aligned to alLeft) to the right of the panel, and finally place another panel (aligned to alLeft or alClient) to the right of the splitter.
Set MinSize to specify a minimum size the splitter must leave when resizing its neighboring control. Set Beveled to True to give the splitter's edge a 3D look.