HTML绝对位置会为其子级创建新的定位系统吗？

Question

1. as far as i know, absolute positioned element (.egspan style="position:absolute") will position based on its ancestor's position context, but this absolute positioned element WILL NOT create a new positioning system for its children, is that right?????

2. if #1 is correct, can someone tell me why parent is allowed to set to absolute position in this document? (just search exactly this line in quote will bring you to the relevant paragraph "Specify the parent container as position:relative or position:absolute." http://phrogz.net/css/vertical-align/index.html

parent in that link must be 'relative' right, but not absolute, why does it say absolute is ok? because only relative creates new positioning context, so in that link bullet #3, the top 50% should not work

Answer 1

(1) is not correct. Elements with positioning defined will be positioned relative to the nearest ascestor that has its position set to anything other than static (the defautl).

from: http://www.w3.org/TR/CSS2/visuren.html#absolute-positioning :

In the absolute positioning model, a box is explicitly offset with respect to its containing block. .... An absolutely positioned box establishes a new containing block for normal flow children and absolutely (but not fixed) positioned descendants

Note also: relatively and fixed positioned elements also establish new containing blocks for absolutely positioned elements.