Absolute-block boxes

To compute the static position of a box with a computed value of position:absolute and position-agnostic computed value of display:block (shortened to "absolute-block box"), the user agent will perform layout computation on what is logically a copy of the its containing formatting context. Boxes in this copy are referred to as "hypothetical boxes," while boxes in the original are referred to as "real boxes."

The hypothetical absolute-block box shall be its own statically positioned block formatting context. To compute its used width:

• If the computed value of the width property is set to a value other than auto, use that.
• Otherwise, if the properties left and right are both set, compute the horizontal constraints of the real absolute-inline box, then use its width.
• Otherwise, use the intrinsic width of the real absolute-inline box.

To compute the hypothetical absolute-block box's used height:

• If the computed value of the height property is set to a value other than auto, use that.
• Otherwise, if the properties top and bottom are both set, compute the vertical constraints of the real absolute-block box, then use its height.
• Otherwise, use the intrinsic height of the real absolute-block box.

The hypothetical absolute-inline box shall not have any margins, even if margins are specified. The real absolute-inline box may have margins, subject to the absolute constraint equation.

All other hypothetical boxes will be identical to their real equivalents, except for the effect the presence of the hypothetical absolute-block box has on their layout.

The static position of the real absolute-block box is the absolute position of the hypothetical absolute-block box.

Note: Each absolute-block box's static position is computed using a separate hypothetical formatting context.