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[CSSOMViews] viewport scroll state and the scroll* properties

From: Robert O'Callahan <robert@ocallahan.org>
Date: Thu, 29 Oct 2009 16:31:12 +1300
Message-ID: <11e306600910282031u36e6612ds20b5441831cc1018@mail.gmail.com>
To: Anne van Kesteren <annevk@opera.com>
Cc: www-style <www-style@w3.org>
See http://dev.w3.org/csswg/cssom-view/
Currently it does not define any special handling for the root element and
HTML <body> element. However, all browsers implement some special handling
for these elements, to give access to the viewport scrollbar state.

I've only tested getting and setting scrollTop in HTML. Standards-mode and
quirks-mode testcases attached. Here are the results:
IE8, Firefox (trunk, and many previous versions, I think):
In standards mode, setting scrollTop on the <html> element scrolls the
viewport, and reading it gives the current viewport scroll position. Getting
scrollTop on <body> always returns 0 and setting it does nothing.
In quirks mode, setting scrollTop on the <body> element scrolls the
viewport, and reading it gives the current viewport scroll position. Getting
scrollTop on <html> always returns 0 and setting it does nothing.

Safari 4:
In both standards mode and quirks mode, setting scrollTop on the <body>
element scrolls the viewport, and reading it gives the current viewport
scroll position. Getting scrollTop on <html> always returns 0 and setting it
does nothing.

Opera 10:
In standards mode, setting scrollTop on the <html> OR <body> element scrolls
the viewport. Getting scrollTop on <html> gives the current viewport scroll
position. Getting scrollTop on <body> always returns 0.
In standards mode, setting scrollTop on the <html> OR <body> element scrolls
the viewport. Getting scrollTop on <body> gives the current viewport scroll
position. Getting scrollTop on <html> always returns 0.

I suggest that the IE8/Firefox behaviour be written into the spec. I think
that scrollTop on the root element should work even for non <html> roots and
non-HTML documents, although we don't currently implement this.

I'm not sure what to do about scrollWidth and scrollHeight; looking at the
code they will behave similarly to scrollTop in Firefox --- returning values
from the viewport, instead of the element --- but I haven't tested them.

Rob
-- 
"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
53:5-6]


Received on Thursday, 29 October 2009 03:31:52 GMT

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