262398 - Fixed positioned box is not placed in its containing box

Status: RESOLVED INVALID

(Core :: Layout: Positioned, defect)

Description

[Roland Unger]

User-Agent:       Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.7.3) Gecko/20040910
Build Identifier: Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.7.3) Gecko/20040910

Fixed positioned boxes should have the same bahavior like absolute positioned
boxes - the only difference is the fixing. If the container is not placed in the
top left corner, the positioning is wrong, normally the fixed box is not placed
in its container but in the body container. A work-around is to place the fixed
positioned box in an absolute positioned box without using left and top statements.

Reproducible: Always
Steps to Reproduce:
1. Use the attached file
2.
3.

Actual Results:  
Wrong positions.

Expected Results:  
The same behavior on screen like in the case of absolute positioning but fixed
(and repeated for paged media).

See also: http://www.w3.org/TR/CSS21/visuren.html#fixed-positioning

Comment 1

[Roland Unger]

Attachment: Demonstrations of absolute and fixed positioning

Comment 2

[Gérard Talbot]

There seems to be a misunderstanding.

"the box is fixed with respect to some reference. In the case of continuous
media, the box is fixed with respect to the viewport (and doesn't move when
scrolled)."
http://www.w3.org/TR/CSS2/visuren.html#propdef-position

"the box is fixed with respect to some reference. (...) In the case of handheld,
projection, screen, tty, and tv media types, the box is fixed with respect to
the viewport and doesn't move when scrolled."
http://www.w3.org/TR/CSS21/visuren.html#propdef-position

> Fixed positioned boxes should have the same bahavior like absolute positioned
> boxes - the only difference is the fixing. 

It is not said that the fixing is relative to the offsetParent or its closest
abs. pos. parent in the DOM hierarchy but relative to the viewport. "The only
difference is that for a fixed positioned box, the containing block is
established by the viewport."

> If the container is not placed in the
> top left corner, the positioning is wrong, normally the fixed box is not placed
> in its container but in the body container. 

The specs says relative to viewport, not body container. 

> See also: http://www.w3.org/TR/CSS21/visuren.html#fixed-positioning

At the url you provided, it is said:

"The only difference is that for a fixed positioned box, the containing block is
established by the viewport."

Is this bug related to the 1.7 branch or to the trunk?

Comment 3

[Alexey Chernyak]

I was going to mark this bug INVALID, but the spec does not define behaviour
when no positioning information is given for a fixed or absolute element.

In such case what Mozilla does is positions the box as it would be placed within
normal flow. A fixed box is then fixed in this position inside viewport.

What I understand you propose is that all fixed unpositioned boxes be stacked
one on top of the other in the top left corner of viewport, behaving as if each
of them is a first child of the viewport container?

Note, in your testcase every absolute box has it's positions specified, but only
1 out of 3 fixed boxes does. So saying fixed should have the same behaviour as
absolute doesn't really bring a point across.

Comment 4

[Hixie (not reading bugmail)]

Actually it does, see CSS 2.1 secton 10.3.7.

Comment 5

[Alexey Chernyak]

ok
INVALID then, as current behaviour is per spec.

"For the purposes of calculating the static position, the containing block of
fixed positioned elements is the initial containing block instead of the viewport."

http://www.w3.org/TR/CSS21/visudet.html#abs-non-replaced-width