formula() {
        return new ArgHandler('Cell.formula')
            .case(() => {
                // TODO in future: Return translated formula.
                if (this._formulaType === "shared" && !this._formulaRef) return "SHARED";
                return this._formula;
            })
            .case('nil', () => {
                this.clear();
                return this;
            })
            .case('string', formula => {
                this.clear();
                this._formulaType = "normal";
                this._formula = formula;
                return this;
            })
            .handle(arguments);
    }
Sets the formula in the cell.
@param {string} formula - The formula to set.
@returns {Cell} The cell.