license docs-private export function getSortDuplicateSortableIdError ( id ) { return Error ( `Cannot have two MatSortables with the same id (${ id }).` ) ; } docs-private export function getSortHeaderNotContainedWithinSortError ( ) { return Error ( `MatSortHeader must be placed within a parent element with the MatSort directive.` ) ; } docs-private export function getSortHeaderMissingIdError ( ) { return Error ( `MatSortHeader must be provided with a unique id.` ) ; } docs-private export function getSortInvalidDirectionError ( direction ) { return Error ( `${ direction } is not a valid sort direction ('asc' or 'desc').` ) ; }