253247 - using left:auto or left:0 doesn't consider margin:auto

Status: RESOLVED INVALID

(Core :: Layout: Positioned, defect)

Description

[phrostypoison]

User-Agent:       Mozilla/5.0 (Windows; U; Win98; en-US; rv:1.7) Gecko/20040626 Firefox/0.9.1
Build Identifier: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.7) Gecko/20040626 Firefox/0.9.1

When using left:auto or left:0 on elements with margin:auto, mozilla/firefox
renders incorrectly. See section 10.3.7 of the CSS 2 or 2.1 specification.

Reproducible: Always
Steps to Reproduce:
1. View a page with the description above.

Actual Results:  
the element is positioned to the left.

Expected Results:  
the element should have been centered and margin:auto regarded, according to
section 10.3.7 of the CSS 2/2.1 specification.

Comment 1

[Boris Zbarsky [:bzbarsky]]

Please attach a testcase showing the problem to this bug using
<http://bugzilla.mozilla.org/attachment.cgi?bugid=253247&action=enter>.  As far
as I can tell, this bug worksforme (testcase coming up).

Comment 2

[Boris Zbarsky [:bzbarsky]]

Attachment: Testcase

Comment 3

[Frank Wein [:mcsmurf]]

wfm Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.8a3) Gecko/20040724

Comment 4

[phrostypoison]

It appears that adding a right:0/auto fixes the problem.

Comment 5

[phrostypoison]

Attachment: Original testcase

It appears that mozilla/firefox ignores left:auto.

Comment 6

[Boris Zbarsky [:bzbarsky]]

So.. in your testcase you have left and right both auto (since right is not set
and the initial value is auto), width 100px, and margins auto.  Let's actually
apply the algorithm from section 10.3.7 of the CSS 2.1 specification, shall we?

Starting just below the equation we need to satisfy:

I)   The first paragraph does not apply, since width is not auto
II)  The second paragraph does not apply, since left and right are auto
III) The third paragraph _does_ apply, so both margin-left and margin-right are
     set to 0.

Then we enter the numbered steps:

1) Does not apply
2) Left gets set to the static position (0) and we solve for right.
4-6) Does not apply.

The result is that we have zero left/right margins, left is 0, and right is
whatever is needed to make the equation work.

Marking invalid; our layout of that testcase is exactly correct.