license docs-private export function throwExistingMenuStackError ( ) { throw Error ( 'CdkMenuPanel is already referenced by different CdkMenuTrigger. Ensure that a menu is' + ' opened by a single trigger only.' ) ; } docs-private export function throwMissingPointerFocusTracker ( ) { throw Error ( 'expected an instance of PointerFocusTracker to be provided' ) ; } docs-private export function throwMissingMenuReference ( ) { throw Error ( 'expected a reference to the parent menu' ) ; }