/**
 * For the purposes of this module, an "email address" refers to the Mailbox
 * definition in RFS 5321 section 4.1.2, and NOT to the addr-spec definition
 * found in RFS 5322 section 3.4.1, of which Mailbox appears to be a subset.
 *
 * Ignored by this module is the definition of a "valid email address" given in
 * the HTML Living Standard, which address is (mostly) a subset of Mailbox.
 * https://html.spec.whatwg.org/multipage/input.html#valid-e-mail-address
 *
 * Mailbox is further extended by RFC 6531 (SMTP Extension for
 * Internationalized Email) section 3.3 Extended Mailbox Address Syntax to add
 * support of non-ASCII characters.
 */
/**
 * Type of Mailbox. Flags for buildPattern() and validate() functions.
 */
export declare const enum MailboxType {
    /**
     * RFC 5321 Mailbox address.
     * Does NOT allow quoted string local parts, address literals,
     * or local domains by default. See STRICT flag.
     */
    RFC5321 = 0,
    /**
     * RFC 6531 Extended Mailbox Address (SMTPUTF8 address).
     * Supports Unicode characters.
     * Does NOT allow quoted string local parts, address literals,
     * or local domains by default. See STRICT flag.
     */
    RFC6531 = 1,
    /**
     * Alias to RFC6531.
     */
    SMTPUTF8 = 1,
    /**
     * Add flag to RFC5321 or RFC6531 to allow quoted strings in local part.
     */
    ALLOW_QUOTED_STRING = 2,
    /**
     * Add flag to RFC5321 or RFC6531 to allow address literals.
     */
    ALLOW_ADDRESS_LITERAL = 4,
    /**
     * Add flag to RFC5321 or RFC6531 to allow local domains.
     */
    ALLOW_LOCAL_DOMAIN = 8,
    /**
     * Add flag to RFC5321 or RFC6531 for strict interpretation.
     * (ALLOW_QUOTED_STRING | ALLOW_ADDRESS_LITERAL | ALLOW_LOCAL_DOMAIN)
     */
    STRICT = 14
}
/**
 * True if this environment supports the unicode ('u') flag for RegExp.
 *
 * **Gotcha**: When using in the browser, ensure that the `<script>` is loaded
 * in the UTF-8 `charset` for this constant to reflect the correct value.
 *
 * See [Browser compatibility](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp/unicode#Browser_compatibility).
 * (Hint: Not IE.)
 *
 * https://mathiasbynens.be/notes/es6-unicode-regex
 */
export declare const supportsUnicodeRegExp: boolean;
/**
 * Build a regular expression (RegExp) pattern string for validating/matching
 * an email mailbox address of the given type. Will attempt to use a unicode-
 * aware pattern for SMTPUTF8 addresses if the environment supports it.
 * @see {@link supportsUnicodeRegExp}
 * @param type
 * @returns The regular expression pattern string.
 */
export declare function buildPattern(type?: MailboxType): string;
/**
 * Validate syntax for a RFC 5321/6531(SMTPUTF8) mailbox address.
 * @param mailbox The mailbox address.
 * @param type
 * @returns The normalized, validated mailbox address string
 *          or false on failure.
 */
export declare function validate(mailbox: string, type?: MailboxType): string | false;
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