When an element is called 'positioned' in the visual formatting model, it
may or may not be rendered immediately after the previous element in the
document tree. An element that is positioned ('position' property ) has its
rendering offset from the canvas origin or from its normal flow position
via the 'top', 'right', 'bottom', and 'left' properties.
In addition to determining position offsets, positioning properties also
specify the the visible display area of an element's rendering box ('clip')
and directives indicating what should happen when an element's content
falls outside the rendering box ('overflow'.)
But... positioning in CSS is not just about rendering in 2-dimensions. It also
allows for placement and overlap of elements in an imaginary third dimension
perpendicular to the screen ('z-axis'.)
The final property included in this category, 'vertical-align', is not involved with
"CSS positioning" per se, but it does involve vertical positioning of content
within a rendered line box.
Many of these properties were first introduced prior to CSS2 in the W3C Working
draft "Positioning HTML Elements with Cascading Style Sheets"
Robert Stevahn, Scott Furman, Scott Isaacs, et.al., 19 August, 1997)