/**
 * Renders a duration at the two coarsest units that say something, for a line a reader skims.
 *
 * Truncates at every unit rather than rounding, so a value never reads as more time than elapsed: 90 seconds is
 * `1m 30s`, where rounding would claim `2m`. Below a minute the tenth is kept, since that is the scale at which
 * one check's runtime differs from another's; a whole number sheds the `.0` rather than reading `12.0s`.
 */
export declare function formatDuration(milliseconds: number): string;
/**
 * Renders the clause a skip spends on the time it saved, or `undefined` when there is no saving worth naming.
 * A skip that can say what it saved earns the clause; one that cannot says nothing, and the caller drops it
 * rather than printing a saving of `~0s`.
 *
 * Guards its own input rather than trusting the caller's, because the clause is shared: a non-finite duration
 * compares false against the threshold, and would reach a reader as `saved ~NaNs`.
 */
export declare function formatSaving(milliseconds: number): string | undefined;