/**
 * Bucket key standing in for a null/undefined/empty grouping value. `groupData`
 * already keys that bucket by the empty string; Timeline lanes map their `null`
 * lane key onto it so both share the ordering rule below.
 */
export declare const EMPTY_BUCKET_KEY = "";
/**
 * Order bucket keys for a grouped renderer: declared keys first in the order
 * they are declared, then everything undeclared in first-seen order, then the
 * empty bucket last.
 *
 * `keys` arrives in first-seen order (a `Map`'s key order, which is insertion
 * order), and only keys that are actually present are emitted — a declared
 * value with no rows produces no section and no lane, so ordering never
 * conjures empty bands. The empty bucket is pinned last regardless of where it
 * appears in `order`, so a declared list doesn't have to mention it.
 *
 * Shared by `groupData`, which passes the grouped field's declared `groupOrder`,
 * and by `packLanesBySortValue`, which passes nothing — timeline lanes follow
 * the active sort, so only the empty-bucket-last half of the rule applies
 * there. One field that is both grouped and sorted can therefore rank its
 * sections and its lanes differently; that's the documented contract of
 * `lanePacking="one-per-sort-value"`, not an oversight.
 */
export declare function orderBucketKeys(keys: string[], order?: string[]): string[];
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