[whatwg] Constraint validation for maxlength

Jonas Sicking jonas at sicking.cc
Thu Jul 22 14:46:49 PDT 2010

On Thu, Jul 22, 2010 at 2:18 PM, Aryeh Gregor <Simetrical+w3c at gmail.com> wrote:
> maxlength predates all the other form validation attributes by many
> years.  Historically, browsers would prohibit users from entering text
> beyond the maxlength of an input or textarea, but would not prohibit
> form submission.  HTML5 changes this:
> """
> Constraint validation: If an element has a maximum allowed value
> length, and its dirty value flag is true, and the code-point length of
> the element's value is greater than the element's maximum allowed
> value length, then the element is suffering from being too long.
> """
> http://www.whatwg.org/specs/web-apps/current-work/multipage/association-of-controls-and-forms.html#limiting-user-input-length
> If I read it correctly, this means that pages that previously worked
> no longer will, if a script sets the value of the input to something
> longer than the maxlength.  Something like this was reported against
> Chromium (although in this case it was more of a browser bug for
> autofilling passwords beyond maxlength):
> http://code.google.com/p/chromium/issues/detail?id=45640#c2
> These two test cases show that Opera maintains the legacy behavior
> (not compatible with the spec) and submits the forms regardless of
> maxlength violations, while WebKit (Chromium) blocks submission as
> required by the spec:
> data:text/html,<!doctype html><body
> onload="document.getElementById('a').value='foo'"><form><input id=a
> maxlength=2><input type=submit></form>Try to submit the form
> data:text/html,<!doctype html><form><input id=a><input
> type=submit></form><a href=""
> onclick="document.getElementById('a').maxLength = 2; return
> false">Enter "foo" into the input, click here, then try to submit</a>
> Should the spec (and WebKit) be changed here, or should Opera change?

I think that depends largely on how many, and how big, sites are
affected by this. Do you have a list of known sites with this issue?

/ Jonas

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