/**
 * Implement this interface if you want to add your own custom operator to use with this library.
 */
export interface CustomOperator {
    /**
     * Should return a string that represents the operation and value.  Ex: '=customOperator="abc"'.  The field name will already be prepended to the string
     * before this method gets called.
     * @param value Original value that is passed into the RSQL Filter Expression
     * @param valueString Formatted value that the library uses internally.  This has dates, arrays, booleans, etc in the format that the library uses.
     * @param shouldQuote Boolean passed down to say if this value should be surrounded by quotes.
     */
    convertToRSQLString(value: string | Array<string | number | boolean> | Date | number | boolean | undefined | null, valueString: string, shouldQuote: boolean): string;
}