Using the Right Tag for the Right Job - HTML5 Mastery: Semantics, Standards, and Styling - page 50

The type attribute specifies the MIME type of the resource being linked. It is purely
advisory to the browser (for example, the user agent won't solely rely on the value spe-
cified here to determine the resource type) and can be omitted for style sheets since they
are the most commonly encountered type of file used in the link element.
The style element
The style element allows CSS style rules to be embedded directly into an HTML doc-
ument, which may be a quick and convenient way to add style rules when creating a
page, but as with the global style attribute, the CSS styles for a document are best
provided through linking an external style sheet into the page using the link element.
One new attribute is the scoped attribute, which (in theory) allows a piece of generic
CSS to be applied to a specific block of HTML. However, at the time of writing, the
current releases of major web browsers do not support this attribute.
Adding behavior and fallbacks: script and noscript
The script element is like the style and link elements combined, because it sup-
ports writing embedded client-side JavaScript code directly in the HTML document or
allows a script to be loaded as an external file. As with CSS, unless it is unavoidable to
embed the code in the HTML, it is best to place JavaScript in an external file (or files)
that is loaded, like so:
<script type="text/javascript" src="js/menu.js"></script>
The previous code snippet shows the general appearance of the script element
when linking in an external JavaScript file (in this case named menu.js and residing in
a directory named js ). Note that when linking in an external script, the element should
not contain any content between its starting and ending tags.
HTML5 defines a new attribute named async , which in combination with another
attribute, defer , can be used to control when an externally loaded script is parsed.
These are both Boolean attributes, so their presence and absence can affect the loading
of external scripts in various ways ( Table 2-6 ).