[whatwg] overflow of seamless iframes

Robert O'Callahan robert at ocallahan.org
Sun Aug 17 21:03:21 PDT 2008

On Fri, Aug 1, 2008 at 9:11 AM, Ian Hickson <ian at hixie.ch> wrote:

> My original idea (apparently not well conveyed in the spec) is that it
> doesn't actually affect the rendering model at all -- it's still an
> <iframe>, it just doesn't have a border, and the CSS style sheets cascade
> into it and properties inherit into it. So the answer would be "do the
> same as with regular iframes", which I guess is to only support overflow:
> hidden and overflow: visible (and 'auto' mapping to one of those
> dynamically), as derived from the viewport as for any browser context.

I'm not sure what you meant by that. Regular iframes always clip their
contained documents, setting "iframe { overflow:visible; }" won't do
anything. Well, it won't in Gecko; I haven't tested it in other browsers,
but I'd be surprised if they were different.

Note that the default width and height are adjusted for seamless iframes
> to match the width that the element would have if it was a non-replaced
> block-level element with 'width: auto', and the height of the bounding box
> around the content rendered in the iframe at its current width,
> respectively.

"The bounding box" is a bit ambiguous. If the content overflows vertically
above the iframe's viewport, does that contribute to the height of the
bounding box?

For greater seamlessness, I'd prefer to make the intrinsic height be the
height of the iframe's root element. Plus, as dbaron suggested, we'd like
'overflow' to apply to the content of seamless iframes so that horizontal
and vertical overflowing content can be rendered as if the iframe was a
regular overflow:visible block. (We might want to recommend that the UA
style sheet contain "iframe { overflow:hidden; }" to make it easier for
authors to avoid spoofing attacks via seamless sandboxed iframes using
clever positioning.)

"He was pierced for our transgressions, he was crushed for our iniquities;
the punishment that brought us peace was upon him, and by his wounds we are
healed. We all, like sheep, have gone astray, each of us has turned to his
own way; and the LORD has laid on him the iniquity of us all." [Isaiah
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