Data URIs, where the actual images that form the eyes are encoded as data URIs, which allow multimedia to be embedded in web pages rather than stored as a separate file. Acid2 tests the most common case, where a binary image is base64-encoded into text and then that encoded text is included in a data URI in the web page. Although the IETF published the data URI specification in 1998, they never formally adopted it as a standard. Nonetheless, the HTML 4.01 specification references the data URI scheme, and data URI support has now been implemented in most browsers.'Absolute, relative, and fixed CSS positioning, which mean the web developer specifies the exact X and Y coordinates where an element is to be placed into the page, the web developer specifies an X and Y offset from the usual position of the element, and the element is placed relative to the browser window, and scrolls with the window rather than with the rest of the page. The CSS box model, which is a feature that allows the web designer to specify dimensions, padding, borders, and margins, and was the focus of the original Acid1 test. Acid2 not only retests margin support but also tests minimum and maximum heights and widths, features new to CSS 2.0.