PHP and MySQL Web Development 4th Ed-tqw-_darksiderg

858 Chapter 34 Building Web 2.0 Applications with Ajax
by the browser.The developer will have used a bit of JavaScript that sets the CSS attribute
for visibility to visible or not, depending on the actions of the user’s mouse. In an
Ajax-enabled site, it is likely that the area reserved for Section 1 or Section 2 text will be
filled based on the result of a remote scripting call to the server while the rest of the site
remains static.
The Extensible Hypertext Markup Language, or XHTML, functions similarly to
HTML and DHTML in that all three are used to mark up content for display via a
client device (web browser, phone, other handheld device) and allow for the integration
of CSS for additional control of the presentation.The differences between XHTML and
HTML include the manner in which XHTML conforms to XML syntax and the manner
in which XHTML can be interpreted by XML tools in addition to the standard
web-browsing tools.
XHTML is written entirely in lowercase for elements (for example,
instead of ) and attributes (for example, href instead of HREF).
Additionally, all attribute values must be enclosed in either single or double quotation
marks, and all elements must be explicitly closed—either by the end tag in a tag pair or
in singleton elements such as the tag or tag.
For more information on XHTML, see http://www.w3.org/TR/xhtml1/.
Cascading Style Sheets (CSS)
Cascading Style Sheets (CSS) are used to further refine the display of static, dynamic, and
Ajax-enabled pages. Using CSS allows the developer to change the definition of a tag,
class, or ID within one document (the style sheet) and have the changes take effect
immediately in all pages that link to that style sheet.These definitions, or rules, follow a
specific format using selectors, declarations, and values.
n Selectors are the names of HTML tags, such as body or h1 (heading level 1).
n Declarations are the style sheet properties themselves, such as background or
font-size.
n Values are given to declarations, such as white or 12pt.
Thus, the following is a style sheet entry that defines the body of a document as white,
and all text in the document as a normal weight, 12 point,Verdana, or sans-serif font:
body {
background: white [or #fff or #ffffff];
font-family: Verdana, sans-serif;
font-size: 12pt;
font-weight: normal;
}
These values will be in effect for the page until an element is rendered that has its own
style defined in the style sheet. For instance, when an h1 is encountered, the client will