Ben C wrote:
> On 2008-04-05, Gus Richter <gusrichter@netscape.net> wrote:
>> dorayme wrote:
>>> There is a fairly fairly consistent rendering of the phenomenon you have
>>> been wondering about, this is true. So some rules are being followed! I
>>> find the the talk of the various contexts, stacking etc not easy to
>>> negotiate - to be frank.
>> The thing about stacking order for layers is that normally we say that
>> elements must be positioned to overlap in order for any z-index to
>> visually take effect.
>
> Things can overlap quite easily without being positioned, especially
> when overflow and overflow: visible are involved.

I will have to check at a later date about z-index and overflow ...

I was simply saying that "normally" we say ..... Well, here ...

> [...]
>> Well, in the instance of a float we actually already have the float
>> layered on top of the containing block with line boxes (which we've been
>> calling div#shrink in our examples) and regarding this the spec
>> <http://www.w3.org/TR/CSS21/visuren.html#floats> has this to say:
>>
>> "The contents of floats are stacked as if floats generated new
>> stacking contexts, except that any elements that actually create new
>> stacking contexts take part in the float's parent's stacking context.
>> A float can overlap other boxes in the normal flow (e.g., when a
>> normal flow box next to a float has negative margins). When this
>> happens, floats are rendered in front of non-positioned in-flow
>> blocks, but behind in-flow inlines."
>
> The common case of a float on top a box it would be underneath
> (if it didn't get a higher stacking level) is this kind of thing:
>
> <p>
> blah blah
> <span style="float: left; height: 500px; width: 200px"></span>
> blah blah
> </p>
> <p>
> blah blah blah
> </p>
>
> The float sticks out of the bottom of the first P, but is stacked on
> top of the second P, even though the second P comes later in the
> document. Assume P has a non-transparent background in this example.

Even with a background color applied to the float in order to see it,
there is no stacking at all. Am I missing something?

> I think that's the basic reason for giving floats a higher level than
> normal flow blocks.
>
> The inlines go on top of the float but usually they don't need to
> because they flow around it.