/**
 * less-compatible environment lookup.
 *
 * less searches local lesskey variables first, then the real process
 * environment, then system lesskey variables. LESSNOCONFIG filters every
 * lookup except the raw TERM/POSIXLY_CORRECT/platform probes which call
 * `actualEnv` explicitly.
 */
/** A library caller's own value for a variable, if it set one. */
export declare function sessionEnv(name: string): string | undefined;
/**
 * True when the CALLER supplied this variable, rather than it coming
 * from the ambient process environment. The overlay is the embedding
 * application's own configuration, so it can be trusted with choices
 * the surrounding shell cannot be.
 */
export declare function fromSessionEnv(name: string): boolean;
/** Installs (or clears) a library call's environment overlay. */
export declare function setSessionEnv(vars: Record<string, string | undefined> | null): void;
/** Starts a fresh invocation before lesskey tables are loaded. */
export declare function initEnvironment(): void;
/** Clears only lesskey-provided values, used by isolated parser tests. */
export declare function resetLesskeyEnvironment(): void;
/** Adds one #env value to the matching lesskey table. */
export declare function setLesskeyEnv(name: string, value: string, system?: boolean): void;
/** Removes a broken value from the matching lesskey table. */
export declare function deleteLesskeyEnv(name: string, system?: boolean): void;
/** Reads the unfiltered process environment, like less's direct
 *  getenv calls. */
export declare const actualEnv: (name: string) => string | undefined;
/**
 * Reads less's ladder alone: user lesskey #env, then the real process
 * environment, then system lesskey #env, then the compiled defaults.
 *
 * This is what the ENVIRONMENT says with the caller's overlay taken
 * away, so it is the view policy must be read through. A deployment
 * hardens a session through any of these tiers - $LESS in the parent
 * shell, or a #env line in ~/.lesskey - and a library caller may
 * tighten what it finds here but never relax it.
 */
export declare function ambientEnv(name: string): string | undefined;
/**
 * Reads a less environment value with user > process > system precedence.
 * Empty real-environment values are absent, while an empty lesskey value
 * remains a winning table entry just like cmd_decode(EV_OK).
 */
export declare function lgetenv(name: string): string | undefined;
/** TERM uniquely falls back to real getenv even under LESSNOCONFIG. */
export declare const terminalEnv: () => string | undefined;
/** Integer lookup with less's atoi-style invalid fallback. */
export declare function envInteger(name: string, fallback: number): number;
/** Positive millisecond option, preserving the compiled default otherwise. */
export declare function envDelay(name: string, fallback: number): number;
/** True during less's initial no-poll screen-fill grace period. */
export declare function screenFillGrace(): boolean;