We have the maxlength attribute to control the maximum number of characters in an <input> or <textarea>. The minlength attribute is new in HTML5, and is used to specify the minimum number of characters. We definitely need that, please be the first browser to implement it.
UPDATE: The minlength attribute (along with validity.tooShort) is in development for Firefox, enabled by default in Chrome 40, and implemented from Opera 27. Now it's even more important that IE 12 supports it.