2.2.25 [CSS-Level2-2009] Section 9.7, Relationships between 'display', 'position', and 'float'
The specification states:
The three properties that affect box generation and layout — 'display', 'position', and 'float' — interact as follows: If 'display' has the value 'none', then 'position' and 'float' do not apply. In this case, the element generates no box. Otherwise, if 'position' has the value 'absolute' or 'fixed', the box is absolutely positioned, the computed value of 'float' is 'none', and display is set according to the table below. The position of the box will be determined by the 'top', 'right', 'bottom' and 'left' properties and the box's containing block. Otherwise, if 'float' has a value other than 'none', the box is floated and 'display' is set according to the table below. Otherwise, if the element is the root element, 'display' is set according to the table below. Otherwise, the remaining 'display' property values apply as specified.
Quirks Mode (All Versions)
fixed value of the position property is not supported.