/**
 * A formula or a date offset standing in a BRANCH — inside a `<case>`, or as one
 * of the `<gen if="…">` branches of a sequence — rather than as a whole column.
 *
 * Of the four derived constructs, these two read nothing but their own row (see
 * `derived.ts` for the cost model). So a branch can have them as cheaply as a
 * whole column can: for each row the branch holds, compute that row. Measured
 * before this file existed, on all five implementations: a date offset in a
 * branch lost `of=` and `plus=` without a word and drew an unrelated date, and a
 * formula passed `check` and then stopped the run with `gen type "formula" not
 * yet supported` — in four of them; the fifth computed it on one engine only.
 *
 * `running`, `stat`, a formula that reads `prev()` and a pool reference are whole
 * columns by nature, and the validator keeps them out of branches (TDC295,
 * TDC268). They never reach this file.
 */
import type { SequenceBuildContext } from './context.js';
import type { GenSpec, SequenceSpec } from './types.js';
/** A formula, or a date measured from another column: the two that read only their row. */
export declare function isRowLocalDerived(gen: GenSpec): boolean;
/**
 * The branch's values, one per position of the build — or `''` for a row the
 * build will not keep (see `keptRows` on the context).
 */
export declare function rowLocalDerivedValues(gen: GenSpec, count: number, prng: () => number, locale: string, ctx: SequenceBuildContext, instantsOut?: (number | undefined)[]): string[];
/** The context, keeping only `rows` of what it builds — narrowed, never widened. */
export declare function keepingOnly(ctx: SequenceBuildContext, rows: Iterable<number>): SequenceBuildContext;
/**
 * Every column some date offset measures from, wherever the offset stands — a
 * whole column, a `<case>` at any depth, an `if=` branch.
 *
 * Those columns keep the instant they generated beside the text, so the offset
 * works from the value whatever `format=` spelled it as.
 */
export declare function offsetSources(specs: readonly SequenceSpec[]): Set<string>;
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