164983 - default to overflow: auto on postion: fixed elements

Status: RESOLVED INVALID

(Core :: CSS Parsing and Computation, defect)

Description

[Tim Powell]

According to the CSS2 spec, overflow should default to visible so that the full
contents of elements are shown. This works fine in many cases, but with fixed
position elements this can result in a portion of the element being hidden and
impossible to access. If overflow is set to auto on these elements, a scrollbar
will appear when necessary and therefore fix this problem.

In Cascading Style Sheets: Designing for the Web, by Hakon Lie and Bert Bos, it
says "If the contents of the DIV is too large, scroll bars will appear" on page
218. It looks like the intent was for fixed position elements to have overflow:
auto.

This is also more consistent with using position: fixed in place of FRAMEs. With
frames, scrollbars automatically appear when necessary unless authors go out of
their way to disable them (overflow: hidden). It would be nice if position:
fixed had the same behavior by default.

I observed this problem with ASA's blog with Mozilla nightly 2002082208 on
Win2K. With a small enough window or large enough font, some sidebar content
disappears.
http://www.mozillazine.org/weblogs/asa/
This is also reproducable with Debug Viewer Demo #12 More fixed pos. Resize your
window to be smaller and you'll lose part of the sidebar content.

To be complete, bug 105796 asks for the ability to force overflow: auto on ALL
frames, not just by default.

Comment 1

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

This bug is invalid as stated (in proposes a specific, and impossible, technical
solution to a valid problem) but it does raise valid issues.

Comment 2

[Hixie (not reading bugmail)]

Issues which should be raised in www-style, though, not here.

INVALID. WG.

Comment 3

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

I was actually thinking about the fact that we might have serious problems on
'position: fixed' elements with 'overflow: visible' and we need some testcases
(particularly fun mixed-transparency testcases).

Comment 4

[Tim Powell]

David, Why is defaulting overflow to auto technically impossible? Also, what 
does "serious problems on 'position: fixed' elements with 'overflow: visible'" 
mean? Is that a new (potential) bug? Or related to this one? Or just something 
you happened to think of that's not really related? :-)

Ian, I'd appreciate it if you'd raise this issue on www-style. Thanks.

Comment 5

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

Allowing the default value of a property to depend on the value of another
property just isn't the way CSS works.

Not really related.