2.1.54 [CSS-Level2-2009] Section 10.1, Definition of "containing block"
V0211:
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For other elements, if the element's position is 'relative' or 'static', the containing block is formed by the content edge of the nearest block container ancestor box.
Quirks Mode and IE7 Mode (All Versions)
When the position is static,
the containing block is not formed by the content edge of the nearest
block-level ancestor.
V0212:
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If the element has 'position: fixed', the containing block is established by the viewport in the case of continuous media or the page area in the case of paged media.
Quirks Mode (All Versions)
The position: fixed element is not supported.
V0213:
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If the element has 'position: absolute', the containing block is established by the nearest ancestor with a 'position' of 'absolute', 'relative' or 'fixed', in the following way: 1. In the case that the ancestor is an inline element, the containing block is the bounding box around the padding boxes of the first and the last inline boxes generated for that element. In CSS 2.1, if the inline element is split across multiple lines, the containing block is undefined. 2. Otherwise, the containing block is formed by the padding edge of the ancestor. If there is no such ancestor, the containing block is the initial containing block.
Quirks Mode (All Versions)
None of these statements are supported.