valFn = function (v, ctx) {
            if (v == null) return true;
            if (typeof (v) !== "string") return false;
            return v.length <= ctx.maxLength;
        }
Returns a standard maximum string length Validator; the maximum length 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 less than or equal to 5 characters.
        regionProperty.validators.push(Validator.maxLength( {maxLength: 5}));
    @method maxLength
    @static
    @param context {Object} 
    @param context.maxLength {Integer}
    @return {Validator} A new Validator