[whatwg] Comments on <dialog>

Matt Falkenhagen falken at chromium.org
Sun Apr 21 21:35:45 PDT 2013

I've been working on implementing <dialog> for Blink. Here are some
questions and feedback.

1. Browsers that don't support <dialog> will show the content by
default, unlike browsers that do. Should the spec be changed to make
dialogs open by default (and use a "closed" instead of "open"
attribute)? Or is there another easy way to degrade gracefully for
older browsers?

2. Would naming the methods open/close or show/hide instead of
show/close be more natural?

3. For centering in the viewport, the spec mandates that the used
value of 'top' be specially calculated. I found it more convenient to
implement by mutating the computed value rather than the used value.
This has the added benefit that it's straightforward for the page
author to implement dragging using getComputedStyle.

4. Why isn't the dialog horizontally centered in the viewport? The
spec just mentions vertical centering and 'top'.

5. For centering, the spec may need to be more detailed about what
happens in different writing modes. Probably we want to center
horizontally in vertical writing mode, in which case we don't set

6. If I understand the spec correctly, a dialog doesn't escape its
iframe and particularly a modal dialog in an iframe doesn't block the
iframe's parent browsing context's document. Is that accurate? I
wonder if there are use cases we should support for escaping an iframe
(perhaps just seamless ones).

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