_enterFormulaMode() {
        if (this.settings.formulaMode) {
            this.formulaMode = true; // 'Deactivate' the normal event listeners behavior
            // Clear the input and add a '=' sign to it
            AutoNumericHelper.setElementValue(this.domElement, '=');
            // Put the caret after the `=` character
            AutoNumericHelper.setElementSelection(this.domElement, 1);
        }
    }
Enter the special 'formula mode' where users can enter a math expression that will be evaluated on blur and `enter`
@private