Gets or sets the URL of the Web page to post to from the current page when the button control is clicked.
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You can use the IButtonControl.PostBackUrl property to perform a cross-page post. If the IButtonControl.PostBackUrl property is set to the page that the button is currently on, a normal postback event cycle occurs.
A control that implements the System.Web.UI.WebControls.IButtonControl interface must implement the IButtonControl.PostBackUrl property to indicate the URL of the Web page to post to from the current page when the button control is clicked.