These eight units were a feature of CSS 1 and retained in all subsequent revisions. The proposed CSS Values and Units Module Level 3 will, if adopted as a W3C Recommendation, provide seven further length units: codice_16; codice_17; codice_18; codice_19; codice_20; codice_21; and codice_22. Before CSS, nearly all presentational attributes of HTML documents were contained within the HTML markup. All font colors, background styles, element alignments, borders and sizes had to be explicitly described, often repeatedly, within the HTML. CSS lets authors move much of that information to another file, the style sheet, resulting in considerably simpler HTML. For example, headings (codice_23 elements), sub-headings (codice_24), sub-sub-headings (codice_25), etc., are defined structurally using HTML. In print and on the screen, choice of font, size, color and emphasis for these elements is "presentational". Before CSS, document authors who wanted to assign such typographic characteristics to, say, all codice_24 headings had to repeat HTML presentational markup for each occurrence of that heading type. This made documents more complex, larger, and more error-prone and difficult to maintain. CSS allows the separation of presentation from structure. CSS can define color, font, text alignment, size, borders, spacing, layout and many other typographic characteristics, and can do so independently for on-screen and printed views. CSS also defines non-visual styles, such as reading speed and emphasis for aural text readers. The W3C has now deprecated the use of all presentational HTML markup. For example, under pre-CSS HTML, a heading element defined with red text would be written as:   Chapter 1. Using CSS, the same element can be coded using style properties instead of HTML presentational attributes:   Chapter 1. The advantages of this may not be immediately clear but the power of CSS becomes more apparent when the style properties are placed in an internal style element or, even better, an external CSS file. For example, suppose the document contains the style element:  h1 {  All codice_23 elements in the document will then automatically become red without requiring any explicit code. If the author later wanted to make codice_23 elements blue instead, this could be done by changing the style element to:  h1 {  rather than by laboriously going through the document and changing the color for each individual codice_23 element.