how to close a sharepoint modal dialog

SP.UI.ModalDialog.commonModalDialogClose(SP.UI.DialogResult.OK, "some string here")

For example...

SP.UI.ModalDialog.commonModalDialogClose(0,'Canceled the dialog.'); is like using SP.UI.DialogResult.cancel

SP.UI.ModalDialog.commonModalDialogClose(1,'Yay Success!'); is like using SP.UI.DialogResult.OK

SP.UI.ModalDialog.commonModalDialogClose(-1,'Uh oh... Error'); is like using SP.UI.DialogResult.invalid