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/*!

\page qtwebkit-guide-css.html

\title Level 3 CSS (BETA)

\chapter Level 3 CSS
This section of the Qt WebKit Guide serves as an introduction to various Level 3 CSS features
supported by QtWebKit:

\list

\o The \l{Media Queries} section discusses a simple client-based technique to
present different interfaces and functionality from a single source of content
to different classes of mobile device.

\o The \l{Selectors} section concentrates on recently introduced syntax elements
that make applying formatting and gathering DOM elements more flexible.

\o The \l{Visual Effects} section surveys numerous formatting properties,
including new color models and advanced WebKit effects.

\o Finally, the \l{Dynamic CSS} section discusses 2D transforms, transitions,
and keyframe animations.

\endlist

This section features links to numerous sample pages that demonstrate how
various CSS3 features may be applied within a mobile interface. For best
results, view these samples with a modern Webkit-based browser such as Apple
Safari or Google Chrome. Resize the window in which the sample appears to
roughly match the dimensions of a touch-screen mobile device.

\section1 Media Queries

CSS \e{media queries} extend \e{media types} with more detailed capabilities.
Media queries offer a simple client-side mechanism to customize interfaces
comprehensively via CSS.

Media queries are especially useful when extending a body of content for
presentation on mobile browsers. Prior to support for this feature, there were
two basic approaches to provisioning mobile web content, both server-based:

\list
\o \e{Mobile-specific domains}. Content providers might provide a separate
access points for default content at \c{www.website.com}, with mobile content
available at \c{m.website.com} or \c{website.mobi}. There might also be an
additional \c{touch.website.com} access point targeted for higher-end
touch-screen browsers.

\o \e{Dynamic Server-based Adaptation}. In this case, there is a single access
point, but the server sends different content, typically depending on the
\e{User-Agent} header included in all browsers' HTTP requests.
This approach may leverage databases of device characteristics such as
\l{WURFL} or \l{DeviceAtlas}.
\endlist

This section describes how to provision CSS entirely on the mobile
client.

    \section2 Media Types and Media Queries

    If you only want to serve interfaces for desktop browsers and low-end mobile
    browsers, specify external CSS files within your HTML's \c{head} region
    using media types:

    \code
    <link media="screen" href="/path/to/desktop.css" type="text/css" rel="stylesheet"/>
    <link media="handheld" href="/path/to/mobile.css" type="text/css" rel="stylesheet"/>
    \endcode

    The \c{media} attribute specifies different \e{types} of browser: \c{screen}
    for large-screen desktop browsers, and \c{handheld} for mobile browsers.
    Browsers identifying themselves as \c{handheld} are served the
    \c{mobile.css} file, which should specify a dramatically simplified
    mobile interface.

    A problem arises, however, when the majority of higher-end touch browsers
    identify themselves as the \c{screen} media type, to avoid being served
    overly simplified content that is beneath their capabilities. The example
    above serves a desktop-oriented design to later-generation mobile browsers.
    To target a higher-end mobile design to these browsers, you need to specify
    additional media \c{queries}:

    \code
    <link media="only screen and (min-device-width: 481px)" href="/path/to/desktop.css" type="text/css" rel="stylesheet"/>
    <link media="only screen and (max-device-width: 480px)" href="/path/to/touch.css" type="text/css" rel="stylesheet"/>
    <link media="handheld" href="/path/to/mobile.css" type="text/css" rel="stylesheet"/>
    \endcode

    The first two lines specify any \c{screen}-typed browser whose window
    is wider or narrower than 480 pixels.

    Regions of content that are inappropriate for presentation within
    either the touch-based or lower-end mobile design can then be easily
    removed within the corresponding CSS files:

    \code
    .widget, .nested_nav, .sidebar, .video_ad, .related_items {
        display: none;
    }
    \endcode

    The following example demonstrates a simple message identifying your class
    of browser, which appears dynamically based on CSS that is linked using
    media types and media query syntax:

    \l{mob_mediaquery}{\inlineimage webkit-guide/scr_mob_mediaquery.png
    }

    \e{Click on the image to view the example live in a browser or click on the
    following links to view the CSS files.}

    \l{mq_desktop_css}{(Desktop CSS)}
    \l{mq_touch_css}{(Touch-Screen CSS)}
    \l{mq_mobile_css}{(Low-end Mobile CSS)}

    The following example shows a skeletal interface that appears differently
    based on the type of browser viewing it. The image below shows how it
    appears when viewed on a touch-based browser, but a desktop browser renders
    a more elaborate three-column layout:

    \l{mob_layout}{\inlineimage webkit-guide/scr_mob_layout.png
    }

    \l{mqlayout_desktop_css}{(Desktop CSS)}
    \l{mqlayout_touch_css}{(Touch-Screen CSS)}
    \l{mqlayout_mobile_css}{(Low-end Mobile CSS)}

    When viewed with a desktop browser,
    the page displays a typical desktop-style layout:
    a main content column surrounded by navigation and sidebar columns,
    with banner headers and footers that straddle the top and bottom of
    the screen.
    When viewed with a touch-based browser,
    the sidebar element does not appear.
    The main content extends to the full width of the screen,
    while header and navigation elements share the top of the screen.
    When viewed with other mobile browsers,
    even the top of the screen is simplified to replace header information
    with a simple icon.

    Note that you can also use media queries to customize interfaces for
    tablet devices such as the Apple iPad:

    \code
    <link rel="stylesheet" media="all and (min-device-width: 481px)
        and (max-device-width: 1024px)" href="/path/to/ipad.css"/>
    \endcode

    \section2 In-line Media Queries

    While it's generally good practice to keep CSS for different designs within
    separate files, you can also consolidate them. The following example
    provides a default san-serif font styling for \c{h1} elements, then
    different sets of style sheets for three browser categories:

    \code
    h1 { font-family : Arial, sans-serif }
    @media screen {
        h1 { color: #00008B; }
    }
    @media only screen and (max-device-width: 480px) {
        h1 { color: #00008B; font-size: medium; }
    }
    @media handheld {
        h1 { font-size: medium; font-weight: bold }
    }
    \endcode

    Consolidating style sheets in this manner may reduce the number of separate
    HTTP requests, help web designers to keep track of variations among designs,
    and reduce style sheet properties defined redundantly in more than one file.

    \section2 Media Queries via JavaScript

    Browsers that support media queries also support APIs to test them from
    within JavaScript. Browsers based on QtWebKit use the \c{matchMedia} API.
    Some other browsers use a slightly different (and older) \c{styleMedia} API,
    which itself used to be called the \c{media} API. Each can be called from
    the \c{window} object. The following function accounts for all three cases:

    \code
    function matchesMediaQuery(query) {
        if (!!window.matchMedia)
            return window.matchMedia(query).matches;
        if (!!window.styleMedia && !!window.styleMedia.matchMedium)
            return window.styleMedia.matchMedium(query);
        if (!!window.media && window.media.matchMedium)
            return window.media.matchMedium(query);
        return false;
    }
    \endcode

    The \c{query} argument corresponds to the media query string used to
    activate the CSS. For example, the following higher-level function tests
    whether the browser matches design categories provided simple labels such as
    \c{desktop}, \c{touch}, or \c{mobile}:

    \code
    function isDesign(str) {
        var design;
        if (matchesMediaQuery('only screen and (min-device-width: 481px)')) {
            design = 'desktop';
        }
        else if (matchesMediaQuery('only screen and (max-device-width: 480px)')) {
            design = 'touch';
        }
        else if (matchesMediaQuery('handheld')) {
            design = 'mobile';
        }
        return str == design;
    }
    \endcode

    You can then use the test whenever there is a need to assign functionality
    for a specific design. The following gathers a series of images and assigns
    different panel-viewing functions for \c{desktop} and \c{touch} designs,
    with no functionality assigned to the lower-end \c{mobile} design:

    \code
    var imgs = document.querySelectorAll("img.panel");
    for ( var i = 0, len = imgs.length ; i < len ; i++ ) {
        el = imgs[i];
        if ( isDesign("desktop") ) {
            imgs[i].addEventListener("mouseover", showHoverPanel);
            imgs[i].addEventListener("mouseout", hideHoverPanel);
        }
        else if ( isDesign("touch") ) {
            imgs[i].addEventListener("click", showTouchPanel);
        }
    }
    \endcode

    The following example uses this technique to produce a simple message,
    dynamically generated by JavaScript,
    that corresponds to the message generated by CSS:

    \l{mob_condjs}{\inlineimage webkit-guide/scr_mob_condjs.png
    }

    \l{mob_condjs_css}{(CSS)}
    \l{mob_condjs_js}{(JavaScript)}

\section1 Selectors

Level 3 CSS provides many useful new \e{selectors} that make it easier to apply
formatting to page elements. In addition, the \l{Selectors API} makes DOM
elements accessible using the same CSS expressions you use to apply formatting
to them. The following show alternate ways to access elements:

\code
var element = document.getElementById('map');
var element = document.querySelector('#map');

var elements = document.getElementByClassName('active');
var elements = document.querySelectorAll('ul > li.active');
\endcode

This section provides examples of how different kinds of Level 3
selectors might be applied when formatting mobile interfaces.

    \section2 Attribute Matching

    It is often useful to offer visual hints marking different kinds of link.
    Users might want to know the difference between a link to a page on the same
    website and one on an external site. Links to non-HTML file types might pose
    special challenges to mobile users. Alternately, mobile users might get
    special benefit from telephone links.

    You can automate this by using the CSS attribute prefix and suffix matching
    selectors. The following uses \c{^=} to mark external HTTP links, email,
    SMS, and telephone links, by inserting an icon after the text of the link:

    \code
    a[href^="http://"]:after, a[href^="https://"]:after
                             { content : url(icon/external.png); }
    a[href^="mailto:"]:after { content : url(icon/email.png); }
    a[href^="sms:"]:after    { content : url(icon/sms.png); }
    a[href^="tel:"]:after    { content : url(icon/tel.gif); }
    \endcode

    The following uses \c{$=} to identify various file types by common suffixes:

    \code
    a[href$=".doc"]:after { content : url(icon/ms_word.gif) }
    a[href$=".ppt"]:after { content : url(icon/powerpoint.gif) }
    a[href$=".rss"]:after, a[href$=".xml"]:after
                          { content : url(icon/feed.gif) }
    a[href$=".pdf"]:after { content : url(icon/pdf.jpg) }
    a[href$=".xls"]:after { content : url(icon/excel.jpg) }
    \endcode

    You can also use \c{*=} to freely match substrings within any attribute
    value. The following might distinguish links to a site's blog area based on
    how the URL is organized:

    \code
    a[href*="/blog/"]:after { content : url(icon/blog.jpg )}
    \endcode

    The following example demonstrates links identified by dynamically generated
    icons:

    \l{layout_link-fmt}{\inlineimage webkit-guide/scr_layout_link-fmt.png
    }

    \l{layout_link-fmt_css}{(CSS)}

    \section2 Form Input State

    The \c{:checked} dynamic class allows you to style radio and checkbox inputs
    based on their selection state:

    \code
    input[type=radio],
    input[type=checkbox]
    { text-align : right }

    input[type=radio]:checked,
    input[type=checkbox]:checked
    { text-align : left }
    \endcode

    This enables the following mobile-friendly interface, which converts small
    radio and check boxes to much more accessible toggle buttons:

    \l{form_toggler}{\inlineimage webkit-guide/scr_form_toggler.png
    }

    \l{form_toggler_css}{(CSS)}

    Using the dynamic \c{:checked} CSS class, the \c{text-align} property
    toggles from \c{left} to \c{right} depending on whether the \c{input} is
    checked or not. Note that to display button text, dynamic classes can be
    chained together to form complex expressions:
    \c{input[type=radio]:checked:before}.

    The example also relies on the \c{-webkit-appearance} property, which allows
    you to override the default visual presentation of specialized interface
    elements such as radio and checkbox inputs.

    The following example provides alternate styling for radio and checkbox
    inputs, presenting them as tappable buttons:

    \l{form_tapper}{\inlineimage webkit-guide/scr_form_tapper.png
    }

    \l{form_tapper_css}{(CSS)}

    Form elements may also be re-styled based on whether they are \c{:enabled}
    or \c{:disabled}. In addition, the \c{:focus} dynamic class allows you to
    style text form inputs or other editable content regions that users have
    currently selected for editing.

    \section2 Navigational Selectors

    Elements within a page that are the target of navigation can receive
    distinct styling using the \c{:target} dynamic class. The act of navigating
    to an element can alter its appearance, or even determine if it is to appear
    at all.

    The following example relies on anchor navigation to display successive rows
    of a table within a mobile interface:

    \l{layout_tbl-keyhole}{\inlineimage webkit-guide/scr_layout_tbl-keyhole.png
    }

    \l{layout_tbl-keyhole_css}{(CSS)}

    While the example relies on table-related tags, they are re-styled with
    block formatting to confine each row of information within the screen. Each
    row features links to other rows, triggering their display. Other links
    navigate away from the table, which suppresses its display altogether. This
    is the main CSS driving the interface:

    \code
    .mobile > tbody > tr        { display : none  }
    .mobile > tbody > tr:target { display : block }
    \endcode

    The same technique may be used to display or dismiss optional interface
    elements such as panels, simply by providing navigation links to them within
    the page.

    \section2 Indirect Sibling Selector

    The Level 2 \c{+} selector allows you to style elements that immediately
    follow other specified elements. For example, the following refers to a
    paragraph that immediately follows a heading at the same level of markup:

    \code
    h1 + p { font-weight: bold }
    \endcode

    In contrast, the Level 3 \c{~} indirect sibling selector allows you to style
    any subsequent element at the same level within the markup. The following
    example styles any element that follows an \c{h2} that is classed
    \c{pullquote}:

    \code
    h2 ~ .pullquote { font-size: 90% }
    \endcode

    \note Webkit-based browsers do not yet allow you to style
    elements dynamically via indirect sibling selectors.

    \section2 Positional Selectors

    Various dynamic classes allow you to style elements depending on their
    position with a series of elements: either elements of the same type, or
    other child elements of the same parent. The following example aligns a
    series of icons to a grid:

    \l{css3_sel-nth}{\inlineimage webkit-guide/scr_css3_sel-nth.png
    }

    \l{css3_sel-nth_css}{(CSS)}

    Columns are specified with the \c{:nth-of-type()} selector, which accepts
    numeric expressions as arguments. The following selectors refer to every
    fourth \c{img} element, but offset by a specified number:

    \code
    img            { position: absolute }
    img:nth-of-type(4n-3)    { left: 2% }
    img:nth-of-type(4n-2)    { left: 27% }
    img:nth-of-type(4n-1)    { left: 52% }
    img:nth-of-type(4n-0)    { left: 77% }
    \endcode

    Alternately, keywords \c{odd} and \c{even} correspond to \c{2n-1} and \c{2n}
    expressions. These are useful, for example, when styling table rows with
    alternating background colors.

    Rows are represented as the number of the element within the series, plus a
    fixed number. Each selector redefines the previous selector's upper range
    of values:

    \code
    img:nth-of-type(n)    { top: 5% }
    img:nth-of-type(n+5)    { top: 20% }
    img:nth-of-type(n+9)    { top: 35% }
    img:nth-of-type(n+13)    { top: 50% }
    img:nth-of-type(n+17)    { top: 65% }
    img:nth-of-type(n+21)    { top: 80% }
    \endcode

    Level 3 CSS defines the following positional selectors:

    \list
    \o \c{:first-child}, \c{:last-child}, and \c{:only-child} refer to the first
    or last child element within a series, or when it is the only one.

    \o \c{:first-of-type}, \c{:last-of-type}, and \c{:only-of-type} refer to the
    first or last specified element within a series, or when it is the only one.

    \o \c{:nth-first-child()} and \c{:nth-last-child()} refer to the specified
    child element positioned from the start or end of the series.

    \o \c{:nth-first-of-type()} and \c{:nth-last-of-type()} refer to the
    specified element positioned from the start or end of the series.

    \o \c{:nth-of-type()} refers to any series of specified elements.

    \o \c{:nth-child()} refers to any series of child elements.

    \endlist

    \section2 Other Selectors

    Level 3 CSS specifies several other potentially useful dynamic
    classes that can be added to selectors:

    \list

    \o \c{:empty} refers to an element that contains no child elements,
    including text nodes.

    \o \c{:root} is a markup-independent way to refer to elements that are
    postioned at the root of the document,
    in most cases the \c{html} tag.

    \o The \c{:not()} dynamic class allows you to narrow a range of
    selectors.
    This may be more useful when gathering elements via the Selectors API.
    For example,
    the following JavaScript gathers form inputs,
    but not including submit buttons:

    \code
    var inputs = document.querySelectorAll("input:not([type=submit])");
    \endcode

    \endlist

\section1 Visual Effects

QtWebKit supports numerous Level 3 CSS visual features. This section briefly
demonstrates how many of these recently available visual features may be used to
refine mobile web designs.

These more advanced CSS3 effects tend to be available only on the latest
generation of mobile browsers. Still, it is safe to use them, even if the design
degrades somewhat for devices that don't support them. When a browser
encounters CSS properties or values it can't interpret, it simply ignores them.
Designers can respond by providing fallback options to allow for \e{graceful
degradation}. For example, the following CSS specifies a plain gray background
in case the browser does not support gradients:

\code
background: #aaaaaa;
background: -webkit-gradient(linear, center top, center bottom,
        from(#777777), color-stop(50%,#dddddd), to(#777777) );
\endcode

Note that many of the CSS properties discussed in this section were implemented
relatively recently, and vendors of browser rendering engines (such as WebKit)
may still be in the process of testing and standardizing their behavior. These
property names feature \e{vendor prefixes} such as \c{-webkit-} for WebKit,
\c{-moz-} for Mozilla, and \c{-o-} for Opera.

It may be possible to extend CSS properties to these various browsers by
providing vendor-specific syntax. The following example shows how to extend the
\c{border-image} property to the Opera browser or Mozilla-based Fennec or the
Maemo Browser for Nokia N900. It also shows the property's final name following
the process of standardization:

\code
-webkit-border-image     : url(img/border-frame.gif) 10 stretch stretch;
-moz-border-image     : url(img/border-frame.gif) 10 stretch stretch;
-o-border-image         : url(img/border-frame.gif) 10 stretch stretch;
border-image         : url(img/border-frame.gif) 10 stretch stretch;
\endcode

In some cases, there are slight variations in the syntax each vendor expects as
property values.

    \section2 Specifying Color and Opacity

    Prior to CSS3, there were three options when specifying color values: named
    colors, hexadecimal color values, or RGB values. CSS3 provides additional
    ways to specify colors:

    \list
    \o \e{HSL}. Colors defined with the HSL model specify the \e{hue} as a
    radial or degree coordinate, then its \e{saturation} and \e{luminence}
    as percentages. The following example specifies red and green values:

    \code
    background: hsl(0  , 100%, 60%);
    background: hsl(128, 75% , 33%);
    \endcode

    \o \e{HSLA}.
    Same as HSL,
    but specifying an additional decimal \e{alpha} value that
    corresponds to opacity.
    The following specifies a fully opaque red,
    followed by a partial transparency:

    \code
    background: hsla(0, 100%, 60%, 1.0);
    background: hsla(0, 100%, 60%, 0.5);
    \endcode

    \o \e{RGBA}.
    Same as RGB,
    but specifying an additional decimal \e{alpha} value that
    corresponds to opacity.
    The following the same transition from opaque to transparent as shown
    above:

    \code
    background: rgba(100%, 0%, 0%, 1.0);
    background: rgba(100%, 0%, 0%, 0.5);
    \endcode
    \endlist

    With the addition of opacity to color definitions, you can now also specify
    \c{transparent} as a color name. Note that while RGBA and HSLA options are
    now available, you can still use the familiar \c{opacity} property
    independently of color definitions.

    \section2 Rounded Corners

    In addition to removing harsh edges, rounded corners often help distinguish
    active items from static background elements. Rounded corners are
    implemented using the \c{border-radius} property. The following rounds off
    an edge to the same extent that interior elements are offset:

    \code
    .rounded {
        border-radius    : 1em;
        padding        : 1em;
    }
    \endcode

    The following example demonstrates how rounded corners can enhance a mobile
    design, by marking the start and end of large regions of content, such as a
    list of links:

    \l{layout_link-fmt}{\inlineimage webkit-guide/scr_layout_link-fmt.png
    }

    \l{layout_link-fmt_css}{(CSS)}

    The greater the measurement applied to an element's \c{border-radius}, the
    more dramatically rounded are its corners. For example, applying a
    \c{border-radius} that is half an element's overall dimensions results in a
    circle:

    \code
    .circle {
        width              : 4em;
        height             : 4em;
        border-radius      : 2em;
    }
    \endcode

    You can also set each corner individually, and specify a pair of values to
    achieve oval-shaped borders:

    \code
    border-top-left-radius : 2em/1em;
    \endcode

    \section2 Border Images

    Border images allow you to apply customized marquee effects, as in the
    following example:

    \l{css3_border-img}{\inlineimage webkit-guide/scr_css3_border-img.png
    }

    \l{css3_border-img_css}{(CSS)}

    In this case, the image stretches to fit an element's dimensions:

    \code
    -webkit-border-image : url(img/border-frame.gif) 10 stretch stretch;
    \endcode

    As is true of the \c{border} property, a single numeric argument specifies
    the width of the border as a whole, or up to four values to modify the width
    of each side.

    Any border image you specify substitutes some or all of an element's normal
    border. The \c{border-image} and \c{border-corner-image} each collectively
    represent four more specific properties.

    For \c{border-image}, these properties are:

    \list
    \o \c{border-top-image}
    \o \c{border-right-image}
    \o \c{border-bottom-image}
    \o \c{border-left-image}
    \endlist

    For \c{border-corner-image}, these properties are:
    \list
    \o \c{border-top-left-image}
    \o \c{border-top-right-image}
    \o \c{border-bottom-right-image}
    \o \c{border-bottom-left-image}
    \endlist

    The \c{border-image} property specifies a single image for all four edge
    borders. The \c{border-corner-image} property specifies an image for all
    four corner borders. To specify images individually for any of the edge or
    corner borders, use any of the eight individual properties.

    When specifying any border edge or corner image values:

    \list
    \o A \c{stretch} value stretches one image to fill the element border area,
    as shown in the example above.

    \o A \c{repeat} value repeats one image until it fills the element border
    area and clips any overflow, for example:

    \code
    -webkit-border-image : url(img/border-frame.gif) 10 repeat repeat;
    \endcode

    In this case the first \c{repeat} applies to top and bottom edge borders,
    and the second applies to left and right edge borders.
    \endlist

    \section2 Backgrounds

    CSS3 allows you to specify more than one background image at a time.
    The following example shows an accordion-style tabbed interface:

    \l{css3_backgrounds}{\inlineimage webkit-guide/scr_css3_backgrounds.png
    }

    \l{css3_backgrounds_css}{(CSS)}
    \l{css3_backgrounds_js}{(JavaScript)}

    By default, tabs display a single icon image, but when selected feature an
    additional gradient background image. The following CSS shows how both icon
    and background can receive their own series of specifications, affecting
    their offset or whether each image repeats:

    \code
    background-image    : url(img/select.png)    , url(img/gradient.jpg);
    background-repeat    : no-repeat        , repeat-x;
    background-position    : 12px 12px        , 0 0;
    \endcode

    In addition, you may set the \c{background-size} property to \c{contain} to
    scale images to the size of the containing element. (Level 2 CSS allowed
    only specific measurements or percentages of the image's size.)

    \section2 Text Shadow and Stroke

    Shadows can be applied to text. As the following example shows, text shadows
    may interfere with the legibility of text, and are seldom appropriate unless
    they're used for large, sans-serif display headings:

    \l{css3_text-shadow}{\inlineimage webkit-guide/scr_css3_text-shadow.png
    }

    \l{css3_text-shadow_css}{(CSS)}

    In addition to the shadow's color, the property accepts two measurements to
    represent its offset from the text, while the third specifies the extent to
    which the shadow is blurred:

    \code
    h1,h2,h3,h4 { text-shadow : 0.25em 0.25em 0.25em #aaaaaa; }
    \endcode

    CSS3 also allows you to apply a different colored fill to characters,
    suitable mainly for larger display type or subtle animations:

    \l{css3_text-stroke}{\inlineimage webkit-guide/scr_css3_text-stroke.png
    }

    \l{css3_text-stroke_css}{(CSS)}

    In the following CSS, \c{-webkit-text-fill-color} is synonymous with the
    standard \c{color} property:

    \code
    -webkit-text-stroke-color    : #000000;
    -webkit-text-stroke-width    : 1px;
    -webkit-text-fill-color        : purple;
    \endcode

    \section2 Text Overflow

    Web developers are familiar with the \c{overflow} property, which can be
    used to hide content that exceeds an element's dimensions, or else to make
    it accessible via scrolling. CSS3 specifies an additional \c{text-overflow}
    property that allows you to add ellipses as a suffix to any text that
    overflows the element, to indicate the presence of additional text.

    The following example shows how the \c{text-overflow} property allows you to
    present user-selectable links to expanded regions of text within a page:

    \l{css3_text-overflow}{\inlineimage webkit-guide/scr_css3_text-overflow.png
    }

    \l{css3_text-overflow_css}{(CSS)}
    \l{css3_text-overflow_js}{(JavaScript)}

    Use the \c{text-overflow} property in conjunction with \c{overflow} and
    \c{white-space}:

    \code
    text-overflow    : ellipsis;
    overflow    : hidden;
    white-space    : nowrap;
    \endcode

    For \c{text-overflow} to work, the element's \c{white-space} must be set to
    \c{nowrap}, overriding the default \c{normal} value. This prevents words
    from wrapping onto another line as is standard behavior outside the \c{pre}
    tag, and forces text past the right edge of the element.

    (The element's \c{text-overflow} may specify both \c{ellipsis} and
    \c{ellipsis-word}, the latter of which is not as widely implemented.)

    \section2 Custom Scrollbars

    In general, scrollable elements should be avoided wherever possible within
    mobile interfaces. Drag gestures already allow users to scroll windows
    vertically, and narrow mobile screens are not suitable for overly wide
    content.

    In cases where content can only be viewed within a scrolling window,
    scrollbars can be reformatted to make them more accessible to mobile users.
    The following example presents a block of code within a touch-enabled mobile
    interface:

    \l{css3_scroll}{\inlineimage webkit-guide/scr_css3_scroll.png
    }

    \l{css3_scroll_css}{(CSS)}

    This interface uses standard scrollbars, but their appearance is enhanced
    using low-level \e{pseudo-element} CSS classes that refer to individual
    components within the scrollbar.

    Simply by invoking the following CSS selector, you disable scrollbars'
    default appearance:

    \code
    pre::-webkit-scrollbar { height : 3em }
    \endcode

    In this case, the specified property increases the scrollbar's default
    \c{height} to make it easier for mobile users to tap it with their fingers.

    Each additional scrollbar component must then be explicitly defined,
    otherwise it does not render. The following CSS provides custom styling for
    the horizontal panning buttons:

    \code
    ::-webkit-scrollbar-button:increment {
        background-image    : url(img/arrow_right.png);
        background-size    : contain;
        background-repeat    : no-repeat;
        width        : 3em;
        height        : 3em;
    }
    ::-webkit-scrollbar-button:decrement {
        background-image    : url(img/arrow_left.png);
        background-size    : contain;
        background-repeat    : no-repeat;
        width        : 3em;
        height        : 3em;
    }
    \endcode

    In this case, the scrollbar region between the two navigation icons is still
    active, but not obviously so since its visual formatting has been
    overridden. The simpler set of controls is far more suitable for a mobile
    interface.

    Webkit provides pseudo-elements for the following components:

    \list
    \o \c{scrollbar} refers to scrollbar as a whole. Additional dynamic classes
    can be appended to specify \c{:vertical} and \c{:horizontal} scrollbars. The
    \c{:corner-present} dynamic class activates when both scrollbars are
    present.

    \o \c{scrollbar-button} refers to incremental navigation buttons. Each
    button can be styled separately with \c{:increment} and \c{:decrement}
    dynamic classes.

    \o \c{scrollbar-thumb} refers to the scrollbar's slider control.

    \o \c{scrollbar-track} refers to the active navigation region between
    buttons.

    \o \c{scrollbar-track-piece} refers to each portion of the track on either
    side of the thumb control. These can be styled separately using \c{:start}
    and \c{:end} dynamic classes.

    \o \c{scrollbar-corner} refers to the corner where scrollbar tracks meet.
    The \c{resizer} pseudo-element also refers to this corner, but for resizable
    elements such as \c{textarea}.

    \o The \c{:double-button} and \c{:single-button} dynamic classes refer to
    whether incrementor and decrementors are paired together redundantly at each
    end of the track, while \c{:no-button} refers to whether they display at
    all.
    \endlist

    \bold{See Also:}
    \l{http://webkit.org/blog/363/styling-scrollbars/}{Surfin' Safari:
    Styling Scrollbars}

    \section2 Gradients

    Gradients provide a graduated shading effect that can add subtle texture to
    background elements, and can provide buttons a three-dimensional, beveled
    appearance. Explicit support for gradients means there's no longer a need to
    implement them as repeating background images.

    Specify gradients using CSS properties such as the following:

    \code
    background: #aaaaaa;
    background: -webkit-gradient(linear, center top, center bottom,
                    from(#dddddd), to(#777777) );
    \endcode

    Note the pair of \c{background} statements. The first specifies a monochrome
    fallback color for browsers that do not support gradients.

    The function specifies a simple \c{linear} gradient from the top to the
    bottom of the element, shifting from a light to a darker gray.

    The following example shows how this gradient can be applied to a background
    element:

    \l{css3_gradientBack}{\inlineimage webkit-guide/scr_css3_gradientBack.png
    }

    \l{css3_gradientBack_css}{(CSS)}

    Gradients cannot be applied to the \c{body} element. Instead, they are here
    applied to an element that covers the background.

    You can specify more than one gradient for the same element. The following
    shifts from a dark to a light gray halfway down the element, then back to
    dark:

    \code
    background: -webkit-gradient(linear, center top, center bottom,
            from(#777777), color-stop(50%, #dddddd), to(#777777) );
    \endcode

    Here is how the additional \c{color-stop} appears when applied to the same
    background element:

    \l{css3_gradientBackStop}{\inlineimage webkit-guide/scr_css3_gradientBackStop.png
    }

    \l{css3_gradientBackStop_css}{(CSS)}

    Gradients can also provide a textured, three-dimensional appearance for
    buttons. In the following example, the gradient is inverted and darkened
    when each button is pressed:

    \l{css3_gradientButton}{\inlineimage webkit-guide/scr_css3_gradientButton.png
    }

    \l{css3_gradientButton_css}{(CSS)}

    In addition to linear gradients, CSS3 also specifies \bold{radial} gradients
    that emanate from a single point. The following example demonstrates a
    colorful radial gradient used to mark where users touch the screen:

    \l{css3_grad-radial}{\inlineimage webkit-guide/scr_css3_grad-radial.png
    }

    \l{css3_grad-radial_css}{(CSS)}
    \l{css3_grad-radial_js}{(JavaScript)}

    The syntax is slightly different than for linear gradients. The first two
    comma-separated arguments after the \c{radial} statement specify the
    coordinates of the inner circle, and its radius. The next two arguments
    specify the coordinates and radius of the outer circle:

    \code
    background: -webkit-gradient(radial, 90 120, 5, 100 130, 48,
            from(#777777), color-stop(50%, #dddddd), to(#777777) );
    \endcode

    The use of \c{from}, \c{to} values and \c{color-stop} in radial gradients
    are the same as for linear gradients.

    \section2 Reflections

    Reflections offer a mirror-like effect which, in the following example, adds
    a sense of weight to headings and images:

    \l{css3_reflect}{\inlineimage webkit-guide/scr_css3_reflect.png
    }

    \l{css3_reflect_css}{(CSS)}

    The property's syntax specifies the edge of the element at which to reflect,
    the offset, and an overlay color. In this case, the color is a gradient,
    which causes the reflection to gradually fade:

    \code
    -webkit-box-reflect : below -0.25em -webkit-gradient(linear, center
                top, center bottom, from(transparent), color-stop(0.25,
                transparent), to(black));
    \endcode

    \section2 Masks

    Masks offer a way to modify an image by overlaying either another image, or
    a gradient. The following example shows a series of thumbnail images that
    appear faded at their bottom edge until selected:

    \l{css3_mask-grad}{\inlineimage webkit-guide/scr_css3_mask-grad.png
    }

    \l{css3_mask-grad_css}{(CSS)}
    \l{css3_mask-grad_js}{(JavaScript)}

    The gradient's opacity shifts from \c 1 to \c 0, an effect that translates
    to the image:

    \code
    -webkit-mask-box-image : -webkit-gradient(linear, left top, left
       bottom, from(rgba(0, 0, 0, 1)), to(rgba(0, 0, 0, 0)));
    \endcode

    The following example demonstrates an image used as a mask to frame another
    image:

    \l{css3_mask-img}{\inlineimage webkit-guide/scr_css3_mask-img.png
    }

    \l{css3_mask-img_css}{(CSS)}

    Separately, the component images look like these:

    \inlineimage webkit-guide/mask0.png
    \inlineimage webkit-guide/mask1.png


    The syntax is the same for border images, and allows you to stretch one
    image over the other:

    \code
    -webkit-mask-box-image : url(img/mask.png) 5% stretch;
    \endcode

\section1 Dynamic CSS

Animations help enhance touch-based mobile interfaces in many ways. They help
ease transitions from one display state to another that might otherwise appear
jarring. They help provide a sense of navigational orientation. They also often
simulate tactile feedback as users' touches result in a tangible visual effect.
Overall, they add a sense of vibrancy that increases users' engagement with the
content on display.

Support by QtWebKit for HTML5 allows you to choose from among several flavors of
web-based animation: Canvas, SVG, and Level 3 CSS. Web developers may also be
familiar with lower-level JavaScript-based animation techniques, which form the
basis of many popular JavaScript libraries such as jQuery and Prototype. This
section focuses on CSS-based animations, since they are more appropriate to
integrate throughout a web design, without the additional overhead JavaScript
libraries require. Like Adobe Flash, SVG and Canvas offer more specialized,
low-level graphics frameworks whose animation features are more appropriate for
generating standalone effects.

This section demonstrates animation techniques by offering a series of examples
that apply to common mobile design tasks. While some of these tasks are
addressed by existing JavaScript frameworks such as jQuery and Prototype, the
examples provided here illustrate some CSS-only alternatives.

    \section2 CSS Animation Concepts

    Level 3 CSS introduces three distinct concepts that are relevant when
    crafting dynamic effects, which are discussed in the following sections:

    \list
    \o \e{Transforms} offer a series of manipulations to screen elements. By
    themselves, transforms present only static visual effects, but they become
    especially useful as part of dynamic transitions and animations. Simple
    transforms are two-dimensional, with three-dimensional transforms gaining
    gradual support.

    \o \e{Transitions} entail a graduated shift from one explicit display
    state to another. Transitional shifts apply to any CSS property that
    specifies numeric or color values.

    \o \e{Animations} offer more complex sequences of transitions that can
    specify many intermediate display states. Unlike simple transitions,
    animations can also be initiated more freely.
    \endlist

    \section2 2D Transforms

    Transforms allow you to freely displace box elements from where they would
    ordinarily appear. Several transform functions are available, allowing you
    to \e{scale}, \e{rotate}, \e{skew}, or \e{translate} (move) objects.

    The \c{translate} function moves an element from its default location, and
    accepts \c{x} and \c{y} measurements as arguments. The following moves an
    element off the right edge of the screen:

    \code
    -webkit-transform: translate(120%, 0);
    \endcode

    Alternately, \c{translateX} and \c{translateY} functions allow you to
    specify each axis independently. This moves the element off the top of the
    screen:

    \code
    -webkit-transform: translateX(0.0) translateY(-120%);
    \endcode

    Scale transforms allow you enlarge or shrink an element, with the scale
    expressed as a decimal. By itself, \c{scale} modifies height and width
    proportionately, but the alternative \c{scaleX} and \c{scaleY} functions
    allow you to constrain scaling to a single axis.

    The following animation demonstrates a \c{translate} function, which moves
    the element from off the screen, followed by series of \c{scale},
    \c{scaleX}, and \c{scaleY} functions:

    \l{anim_demo-scale}{\inlineimage webkit-guide/scr_anim_demo-scale.png
    }

    \l{anim_demo-scale_css}{(CSS)}

    By default, transforms originate from the center of the element, but you can
    specify any edge using the \c{-webkit-transform-origin} property. The
    following reduces an element to 75% of its original size, while keeping it
    at its original bottom edge:

    \code
    -webkit-transform        : scale(0.75);
    -webkit-transform-origin    : bottom;
    \endcode

    The following example uses this scale transform to shrink icons that are
    assigned to in-line links, with icons aligning to the text's baseline:

    \l{layout_link-fmt}{\inlineimage webkit-guide/scr_layout_link-fmt.png
    }

    \l{layout_link-fmt_css}{(CSS)}

    The \c{rotate} function accepts degree or radian arguments, with negative
    arguments specifying counter-clockwise motion. The following animation
    demonstrates two rotations: the first clockwise around the element's center
    point, and the second counter-clockwise around the top left corner:

    \l{anim_demo-rotate}{\inlineimage webkit-guide/scr_anim_demo-rotate.png
    }

    \l{anim_demo-rotate_css}{(CSS)}

    The \c{skew} function also accepts positive or negative degree arguments,
    specifying the extent to which to modify the bottom left corner's 90-degree
    angle. The \c{skew} and \c{skewX} functions shift the element horizontally,
    but the alternative \c{skewY} function shifts the element vertically. The
    following animation demonstrates a \c{skewX} followed by a \c{skewY}:

    \l{anim_demo-skew}{\inlineimage webkit-guide/scr_anim_demo-skew.png
    }

    \l{anim_demo-skew_css}{(CSS)}

    In the following example, a variety of transforms make a set of three
    navigational tab icons appear to be part of a cube:

    \l{anim_tabbedSkew}{\inlineimage webkit-guide/scr_anim_tabbedSkew.png
    }

    \l{anim_tabbedSkew_css}{(CSS)}

    The example also implements the tab icons as internal links that activate
    display of content using the \c{:target} dynamic class. See the
    \l{Navigational Selectors} section for more information.

    Note that transforms can include any combination of the functions described
    above:

    \code
    nav > a:nth-of-type(3) {
        background-image    : url(img/S_google.jpg);
        -webkit-transform    : rotate(-60deg) skew(-30deg) translate(1.7em, 0em);
    }
    \endcode

    \section2 Transitions

    Transitions allow you to gradually shift from one defined CSS state to
    another. Any CSS property expressed as a numeric or color value (including a
    color name or hex value) can be transitioned between two style sheets.
    Properties such as \c{display} that have discrete sets of named values, such
    as the \c{display} property's \c{block} or \c{none} values, cannot be
    transitioned. In cases where named values translate internally to numeric
    values, such as the \c{border-width} property's \c{thin} and \c{thick}
    values, they can be transitioned.

    The following example shows a series of transitions from a collapsed icon
    state to an expanded panel:

    \l{anim_panel}{\inlineimage webkit-guide/scr_anim_panel.png
    }

    \l{anim_panel_css}{(CSS)}
    \l{anim_panel_js}{(JavaScript)}

    Each style sheet specifies a different \c{max-width} value, and each
    accompanying transition, defined separately for each state, allows the value
    to shift over the course of half of a second:

    \code
    nav.expanded {
        max-width        : 95%;
        -webkit-transition    : max-width 0.5s ease-in-out;
    }
    nav.collapsed {
        max-width        : 10%;
        -webkit-transition    : max-width 0.5s ease-in-out;
    }
    \endcode

    That shorthand syntax can be expanded to several different properties:

    \code
    nav.expanded {
        max-width                : 95%;
        -webkit-transition-property        : max-width;
        -webkit-transition-duration        : 0.5s;
        -webkit-transition-timing-function    : ease-in-out;
    }
    nav.collapsed {
        max-width                : 10%;
        -webkit-transition-property        : max-width;
        -webkit-transition-duration        : 0.5s;
        -webkit-transition-timing-function    : ease-in-out;
    }
    \endcode

    Available transition functions include \c{linear}, \c{ease-in},
    \c{ease-out}, \c{ease-in-out} and \c{cubic-bezier}.

    Note that the \c{max-width} properties in both style sheets both use
    percentages to specify measurements. Transitions may not work properly if
    you shift from one unit to another.

    The example above specifies an additional set of transitions affecting the
    icons nested within the navigation panel:

    \code
    nav.expanded > .option {
        opacity        : 1;
        -webkit-transform    : scale(1.0);
        -webkit-transition    : all 0.5s linear;
    }
    nav.collapsed > .option {
        opacity        : 0;
        -webkit-transform    : scale(0.0);
        -webkit-transition    : all 0.5s linear;
    }
    \endcode

    The shifting \c{scale} transform makes icons appear to zoom in to fill the
    space, while \c{opacity} makes them fade in. Specifying \c{all} as the
    transition property applies to any valid property that differs between the
    two states.

    These nested transitions execute at the same time as those assigned to the
    parent \c{nav} element. The combined effect appears to be a single
    transition.

    \section2 Transitional Sequences

    The prior example showed a single transition, but transitions can also be
    run in sequence to form more complex animations. The following example
    demonstrates an embedded navigation panel that, when pressed, expands
    horizontally, then vertically to reveal numerous navigation options:

    \l{anim_accord}{\inlineimage webkit-guide/scr_anim_accord.png
    }

    \l{anim_accord_css}{(CSS)}
    \l{anim_accord_js}{(JavaScript)}

    The style sheets specify separate, comma-separated transitions for \c{width}
    and \c{height} properties:

    \code
    #accordion.expanded {
        width: 80%;
        height: 90%;
        -webkit-transition:
            width 0.5s ease-in-out 0.0s,
            height 0.5s ease-in-out 0.5s
        ;
    }
    #accordion.collapsed {
        width: 10%;
        height: 7%;
        -webkit-transition:
            height 0.5s ease-in-out 0.0s,
            width 0.5s ease-in-out 0.5s
        ;
    }
    \endcode

    Each transition's additional time measurement specifies a delay. The
    long-form syntax may make this clearer:

    \code
    #accordion.expanded {
        width: 80%;
        height: 90%;
        -webkit-transition-property        : width        , height;
        -webkit-transition-duration        : 0.5s        , 0.5s;
        -webkit-transition-timing-function    : ease-in-out    , ease-in-out;
        -webkit-transition-delay        : 0.0s        , 0.5s;
    }
    #accordion.collapsed {
        width                : 10%;
        height                : 7%;
        -webkit-transition-property        : height    , width;
        -webkit-transition-duration        : 0.5s        , 0.5s;
        -webkit-transition-timing-function    : ease-in-out    , ease-in-out;
        -webkit-transition-delay        : 0.0s        , 0.5s;
    }
    \endcode

    The shift to the \c{expanded} state involves two transitions, each of which
    lasts half a second and relies on the same \c{ease-in-out} function. The
    first takes place immediately and affects the \c{width} property. The
    second, affecting the \c{height} property, takes place after a delay that
    matches the first transition's duration. The reverse transition is much the
    same, only the \c{height} property transitions before the \c{width} to
    reverse the effect.

    In addition to the navigation element's sequence of transitions, nested
    accordion-style animations activate when users expand top-level headings.
    Subheadings are revealed using a \c{scaleY} transform, which makes them
    appear as if they are flipping upwards.

    The following example shows a photo gallery interface that uses the same
    techniques. (Size the window to emulate a smaller mobile screen.)

    \l{anim_gallery}{\inlineimage webkit-guide/scr_anim_gallery.png
    }

    \l{anim_gallery_css}{(CSS)}
    \l{anim_gallery_js}{(JavaScript)}

    The main interface uses simple transitions affecting \c{opacity}, along with
    \c{scale} and \c{translate} transforms, which combined make queued images
    appear dimmer, smaller, and horizontally offset from the main image.

    A separate sequence of transitions activates when users tap selected images.
    The first transition uses a \c{scaleX} transform to flip the image towards
    the center. The second then flips out a panel featuring details on the
    photo. When users navigate away to adjacent photos, the panel automatically
    flips back to its original state as it is moved to the side.

    Another example shows an interface featuring a simple list of items:

    \l{anim_skew}{\inlineimage webkit-guide/scr_anim_skew.png
    }

    \l{anim_skew_css}{(CSS)}
    \l{anim_skew_js}{(JavaScript)}

    When dismissed, items are wiped off the screen using a \c{skew} transform
    that provides the illusion of speed. Remaining items move upwards to fill
    the space vacated by items that have been removed.

    This example uses the same technique of sequential transitions. The first
    transition applies to the combined \c{translate}/\c{skew} transform. The
    second, delayed transition modifies the \c{top} property to align remaining
    items to a grid.

    Note that for items to reposition themselves in this example, a vertical
    grid must be explicitly specified. You can only apply transitions between
    properties you explicitly define and activate, not between values the
    browser assigns internally to automatically position elements relative to
    each other.

    \section2 Keyframe Animations

    The previous section showed how you can chain sequences of transitions to
    produce complex effects. Animations also allow you to define many
    intermediary interface states, but using a far simpler syntax, and not
    assigned to transitions between CSS states.

    The following example shows a simple animation of icons that pulse when
    selected:

    \l{anim_pulse}{\inlineimage webkit-guide/scr_anim_pulse.png
    }

    \l{anim_pulse_css}{(CSS)}

    It uses the following CSS, shown here in both abbreviated and long form:

    \code
    nav > a:target { -webkit-animation : pulse 1s infinite; }

    nav > a:target {
        -webkit-animation-name        : pulse;
        -webkit-animation-duration        : 1s;
        -webkit-animation-iteration-count    : infinite;
    }
    \endcode

    You supply a \c{name} for the animation that corresponds to a
    \c{keyframes} rule defined separately within your CSS:

    \code
    @-webkit-keyframes pulse {
        0% { opacity : 1.0 }
        50% { opacity : 0.7 }
    }
    \endcode

    Percentages mark new animation states within the course of the animation,
    and behave much like CSS selectors. In this case, the animation shifts
    between two separate states over the course of a second: opaque and slightly
    dimmed. With its \c{iteration-count} set to \c{infinite} rather than a set
    number, the animation only stops when the link is no longer selected.

    The following example demonstrates a popular mobile design pattern
    implemented with CSS. Navigation to nested subheads appears to wipe to the
    right, while navigating upwards in the hierarchy appears to wipe to the
    left:

    \l{anim_slide1}{\inlineimage webkit-guide/scr_anim_slide1.png
    }

    \l{anim_slide_css}{(CSS)}

    It relies on keyframes rules such as the following, which define a simple
    start and end state:

    \code
    @-webkit-keyframes slide_in {
      from {
        left            : 80%;
        right           : -80%;
      }
      to {
        left            : 0em;
        right           : 0em;
      }
    }
    \endcode

    Unlike a transition, the animation is triggered immediately when the page
    loads, but only if the target of navigation is an anchor whose ID is
    \c{in} or \c{out}. If you navigate to the page itself, no animation
    occurs.

    The following example uses a keyframe animation to scroll through banner
    options at the top of the screen:

    \l{css3_multicol}{\inlineimage webkit-guide/scr_css3_multicol.png
    }

    \l{css3_multicol_css}{(CSS)}

    The animation defines a set of rapid shifts alternating with long static
    phases. It modifies the left offset of an element that is five times the
    width of the window.

    \code
    @-webkit-keyframes banner_scroll {
        0% { left    : 0%; }
        18% { left    : 0%; }
        20% { left    : -100%; }
        38% { left    : -100%; }
        40% { left    : -200%; }
        58% { left    : -200%; }
        60% { left    : -300%; }
        78% { left    : -300%; }
        80% { left    : -400%; }
        95% { left    : -400%; }
        100% { left : 0%; }
    }
    \endcode

    Finally, the demonstrations of \l{anim_demo-rotate}{rotate},
    \l{anim_demo-scale}{scale}, and \l{anim_demo-skew}{skew} 2D transforms that
    opened this section all rely on separate keyframe animations to slide in and
    manipulate a series of panels. Separate \c{-webkit-animation-delay} settings
    for each panel control the sequence of each presentation.

*/

/*!
\example webkit/webkit-guide
\title QtWebKit Guide Files
This is a listing of \l{QtWebKit Guide} code.
\note The links to the HTML5 code is found within the guide.
*/