"containing blocks"

[Raffles]

Hi, just a quick question. This is a quote from an article by the Autistic Cuckoo (in the "finally" bit:

If you specify the width for an absolutely positioned element, either
explicitly via width in percents, or implicitly
via left and right, the standard says that it should
be computed relative to the containing block. Both Internet Explorer
and Opera get this wrong, unfortunately, and use the width of the
parent element as the basis for their computations.

What is a "containing block"? Is it simply the "youngest" of the parent elements that has position?

[all4nerds]

Hello

Not sure what Tommy means, the screen left 0 top 0 is the default zero point for absolute position

If you place absolutes in a relative positioned containing block (usually a div) the zero point for the absolutes will be the left top position of the relative containing block

[zcorpan]

See the definition of containing block in the spec.

[Raffles]

Ah, it is to do with whether it has position or not. Thanks for the link.

[AutisticCuckoo]

For a non-positioned element, the containing block is the same as the parent block.

For an absolutely positioned element, the containing block is the nearest positioned ancestor (where 'positioned' means that it has position set to anything but static).

If there is no positioned ancestor, the containing block defaults to the initial containing block. The spec is vague on what that is, but in reality it's the browser viewport.

Elements with position:fixed always use the viewport as its containing block. (Not supported by IE≤6.)