id and class attributes

05:03
The id attribute is used to identify elements and mark up specific functional areas of a
website, and the class attribute is used to classify one or more elements. These important
attributes help you target elements when it comes to styling or scripting. I refer to both of
these attributes throughout the book, but for now all you need to know is that a specific
id attribute value can be used just once per page, whereas a class attribute value can be
used multiple times (the attributes themselves can be used multiple times per page). For

example, say you begin a document with this:
<body id="homepage">

You would then not be able to use an id attribute value of homepage anywhere else on the
same page. However, if you do this:
<body class="homepage">

then you are free to use the class attribute value of homepage as many times as you like
throughout the same page, but bear in mind that it still applies the same CSS, no matter
what tag you apply it to.

<div id="rightColumn">
<strong class="redText">
<p class="big">
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Divs and spans

05:02
Divs and spans are two tags that, when used well, can help give your page a logical structure
and some extra hooks to apply any CSS or DOM scripting that you might need later. When
used badly, they can litter your document unnecessarily and make your markup, styling, and
scripting needlessly complicated.


<div id="header">
...
</div>
<div id="mainContent">
...
</div>
<div id="secondaryContent">
...
</div>
<div id="footer">
...
</div>

A span is used for marking out sections within a block element and sometimes inside
another inline element. It is an inline element, just the same as <em>, <strong>, or <a>,
except without any semantic meaning—it is simply a generic container. It can itself contain
further inline elements, including more spans. For example, say you wish to color the first
two words of a paragraph red, keeping the rest of the paragraph black. You can use a
<span> for this:
<p><span class="leadingWords">The first</span> two words of this å
paragraph can now be styled differently.</p>
A span cannot contain a block element—that is, you cannot place a <div> within a <span>
and expect it to work the way you want.
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CSS and Canvas HTML5

03:39
As with most HTML elements, CSS can be applied to the canvas element itself to add borders, padding,
margins, etc. Additionally, some CSS values are inherited by the contents of the canvas; fonts are a good
example, as fonts drawn into a canvas default to the settings of the canvas element itself.
Furthermore, properties set on the context used in canvas operations follow the syntax you may
already be familiar with from CSS. Colors and fonts, for example, use the same notation on the context
that they use throughout any HTML or CSS document.
Browser Support for HTML5 Canvas
With the arrival of Internet Explorer 9, all browser vendors now provide support for HTML5 Canvas, and
it is already in the hands of a majority of users. This is a major milestone in web development, allowing
2D drawing to thrive on the modern Web.
In spite of the dwindling market share of previous versions of Internet Explorer, it is still a good idea
to first test whether HTML5 Canvas is supported before you use the APIs. The section “Checking for
Browser Support” later in this chapter will show you how you can programmatically check for browser
support.
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Overview of HTML5 Canvas

03:37
When you use a canvas element in your web page, it creates a rectangular area on the page. By default,
this rectangular area is 300 pixels wide and 150 pixels high, but you can specify the exact size and set
other attributes for your canvas element.  A Basic Canvas Element
<canvas></canvas>
Once you have added a canvas element to your page, you can use JavaScript to manipulate it any
way you want. You can add graphics, lines, and text to it; you can draw on it; and you can even add
advanced animations to it.
The Canvas API supports the same two-dimensional drawing operations that most modern
operating systems and frameworks support. If you have ever programmed two-dimensional graphics in
recent years, you will probably feel right at home with the Canvas API because it is designed to be similar
to existing systems. If you haven’t, you’re about to discover how much more powerful a rendering
system can be than the previous images and CSS tricks developers have used for years to create web
graphics.
To programmatically use a canvas, you have to first get its context. You can then perform actions on
the context and finally apply those actions to the context. You can think of making canvas modifications
as similar to database transactions: you start a transaction, perform certain actions, and then commit
the transaction.
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Using the Selectors API HTML5

03:32
getElementById() -Returns the element with the specified id attribute value
<div id="foo">
getElementById("foo");

getElementsByName() -Returns all elements whose name
attribute has the specified value
<input type="text" name="foo">
getElementsByName("foo");

getElementsByTagName() Return all elements whose tag name
matches the specified value
<input type="text">
getElementsByTagName("input");

With the new Selectors API, there are now more precise ways to specify which elements you would
like to retrieve without resorting to looping and iterating through a document using standard DOM. The
Selectors API exposes the same selector rules present in CSS as a means to find one or more elements in
the page. For example, CSS already has handy rules for selecting elements based on their nesting,
sibling, and child patterns.
Read More

CSS File for the HTML5 Page

03:29
body {
background-color:#CCCCCC;
font-family:Geneva,Arial,Helvetica,sans-serif;
margin: 0px auto;
max-width:900px;
border:solid;
border-color:#FFFFFF;
}
header {
background-color: #F47D31;
display:block;
color:#FFFFFF;
text-align:center;
13
}
header h2 {
margin: 0px;
}
h1 {
font-size: 72px;
margin: 0px;
}
h2 {
font-size: 24px;
margin: 0px;
text-align:center;
color: #F47D31;
}
h3 {
font-size: 18px;
margin: 0px;
text-align:center;
color: #F47D31;
}
h4 {
color: #F47D31;
background-color: #fff;
-webkit-box-shadow: 2px 2px 20px #888;
-webkit-transform: rotate(-45deg);
-moz-box-shadow: 2px 2px 20px #888;
-moz-transform: rotate(-45deg);
position: absolute;
padding: 0px 150px;
top: 50px;
left: -120px;
text-align:center;
}
One last thing to keep in mind is that browsers may seem to render things as if they actually
understand these new elements. The truth is, however, that these elements could have been renamed
foo and bar and then styled, and they would have been rendered the same way (but of course, they
would not have any benefits in search engine optimization). The one exception to this is Internet
Explorer, which requires that elements be part of the DOM. So, if you want to see these elements in IE,
you must programmatically insert them into the DOM and display them as block elements.
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