valFn = function (v, ctx) {
            if (v == null) return true;
            if (typeof (v) !== "string") return false;
            if (ctx.minLength != null && v.length < ctx.minLength) return false;
            if (ctx.maxLength != null && v.length > ctx.maxLength) return false;
            return true;
        }
Returns a standard string length Validator; both minimum and maximum lengths must be specified.
    @example
        // Assume em1 is a preexisting EntityManager.
        var custType = em1.metadataStore.getEntityType("Customer");
        var regionProperty - custType.getProperty("Region");
        // Validates that the value of the Region property on Customer will be 
        // between 2 and 5 characters
        regionProperty.validators.push(Validator.stringLength( {minLength: 2, maxLength: 5});
    @method stringLength
    @static
    @param context {Object} 
    @param context.maxLength {Integer}
    @param context.minLength {Integer}
    @return {Validator} A new Validator