Book HomeCascading Style Sheets: The Definitive GuideSearch this book Friday 31st of October 2014 11:44:22 PM

10.8. Media Types and @-rules

Don't get too excited yet. We aren't talking about media types in the sense of things like audio and video authoring. Well, not exactly, anyway. We're talking about creating rules for presentation within various kinds of media. The defined types of media thus far are:

These are all values of @media, one of several new @-rules. Some others are:

10.8.1. Paged Media

Since I just brought up paged media, I should probably mention that there are some new properties that apply to such media. Five of them apply to page breaks and where they appear:

page-break-before
page-break-after
page-break-inside
orphans
widows 

The first two are used to control whether a page break should appear before or after a given element, and the latter two are common desktop publishing terms for the minimum number of lines that can appear at the end or beginning of a page. They mean the same thing in CSS2 as they do in desktop publishing.

page-break-inside (first proposed by this author, as it happens) is used to define whether or not page breaks should be placed inside a given element. For example, you might not want unordered lists to have page breaks inside them. You would then declare UL {page-break-inside: avoid;}. The rendering agent (your printer, for example) would avoid breaking unordered lists whenever possible.

There is also size, which is simply used to define whether a page should be printed in landscape or portrait mode and the length of each axis. If you plan to print your page to a professional printing system, you might want to use marks, which can apply either cross or crop marks to your page. Thus you might declare:

@page {size: 8.5in 11in; margin: 0.5in; marks: cross;}

This will set the pages to be U.S. letter-standard, 8.5 inches wide by 11 inches tall, and place cross marks in the corners of each page.

In addition, there are the new pseudo-classes :left , :right, and :first, all of which are applied only to the @page rule. Thus, you could set different margins for left and right pages in double-sided printing:

@page:left {margin-left: 0.75in; margin-right: 1in;}
@page:right{margin-left: 1in; margin-right: 0.75in;} 

The :first selector applies only to the first page of a document, so that you could give it a larger top margin or a bigger font size:

@page:first {margin-top: 2in; font-size: 150%;}

10.8.2. The Spoken Word

To round things out, we'll cover some of the properties in the area of aural style sheets. These are properties that help define how a speaking browser will actually speak the page. This may not be important to many people, but for the visually impaired, these properties are a necessity.

First off, there is voice-family, which is much the same as font-family in its structure: the author can define both a specific voice and a generic voice family. There are several properties controlling the speed at which the page is read (speech-rate), as well as properties for the pitch , pitch-range, stress, richness, and volume of a given voice. There are also properties that let you control how acronyms, punctuation, dates, numerals, and time are spoken. There are ways to specify audio cues, which can be played before, during, or after a given element (such as a hyperlink), ways to insert pauses before or after elements, and even the ability to control the apparent position in space from which a sound comes via the properties azimuth and

  • When a block-level box is wider than its parent's content area.

  • When an element's box is taller than the height explicitly setfor its parent.

  • When an element has been absolutely positioned.

  • elevation. With these last two properties, you could define a style sheet where the text is read by a voice "in front of" the user, whereas background music comes from "behind" and audio cues come from "above" the user!



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    <IMG SRC="foo.gif" STYLE="clip: rect(10px, auto, auto, 0);">

    The auto values will set the clipping rectangle's bottom to align with the bottom of the image, and the right edge to the right edge of the image. The value of 0 for left keeps the left edge of the clipping rectangle against the left edge of the image, but the 10px for top moves the top edge of the clipping rectangle downward 10 pixels. This will cause the top 10 pixels of the image to become effectively invisible.

    Figure 7-11

    Figure 7-11. Percentage margins and changing environments

    As you can imagine, this leads to the possibility of "fluid" pages, where the margins and padding of elements enlarge or reduce to match the actual size of the display canvas. In theory, as the user changes the width of a browser window, the margins and padding will expand or shrink dynamically -- but not every browser supports this sort of behavior. Still, using percentages for margin and padding may be the best way to set styles that will hold up in more than one media; for example, documents that will

    Figure 7-11

    Figure 7-11. Percentage margins and changing environments

    As you can imagine, this leads to the possibility of "fluid" pages, where the margins and padding of elements enlarge or reduce to match the actual size of the display canvas. In theory, as the user changes the width of a browser window, the margins and padding will expand or shrink dynamically -- but not every browser supports this sort of behavior. Still, using percentages for margin and padding may be the best way to set styles that will hold up in more than one media; for example, documents that will"border-side" properties applies only to a specific side,there isn't any possibility of value replication -- itwouldn't make any sense. There can only be one of each type ofvalue: that is, only one width value, only one color value, and onlyone border style. So don't try to declare more than one valuetype:

    H3 {border: thin thick solid purple;}  /* two width values--WRONG */

    In such a case, the entire statement will be invalid and should beignored altogether.default, this will cause all text in the line to be aligned alongtheir baselines, but of course differentvertical-align values will have different effects.All of the elements could be top-aligned, for example. We'llreturn to vertical alignment later in the chapter, but for now willassume that everything is baseline-aligned.

    Now the line-height comes into play. Let'sassume the following case: