2.1.48 [CSS-Level2-2009] Section 10.3.7, Absolutely positioned, non-replaced elements
The specification states:
5. 'width' is 'auto', 'left' and 'right' are not 'auto', then solve for 'width'
Quirks Mode (All Versions)
Absolutely positioned elements cannot be sized by their
left values. They must have either an intrinsic or specified