Gets or sets the portion of the System.Windows.Forms.ToolStripSplitButton that is activated when the control is first selected.
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If a System.Windows.Forms.ToolStripSplitButton has a ToolStripSplitButton.DefaultItem, the ENTER key activates the button. Otherwise, the ENTER key activates the drop-down.
Use the ToolStripSplitButton.DefaultItem property to synchronize the Control.Click event of the chosen drop-down item with the item shown on the button.