Tuesday 07th of February 2012 05:23:34 AM
XHTML: What is XML?
XML (Extensible Markup Language) is a “super” markup language from which programmers can develop other, custom markup languages and specialized applications. XHTML (Extensible Hypertext Markup Language) is one such markup language.
Programmers already use XML for database and catalog work, and XML also acts as the foundation for standard web protocols including Scalable Vector Graphics (SVG), Synchronized Multimedia Integration Language (SMIL), Wireless Markup Language (WML), and Platform for Privacy Preferences (P3P).
For information about these web protocols, visit W3C.
« XHTML Section Index | XHTML Guidelines »
Negative margins have an impact on vertical formatting, affecting how
margins are collapsed. If there are negative vertical margins, then
the browser should take the absolute
maximum of the negative margins and subtract that from the maximum of
any positive margins.
In the case where there are only two margins to be collapsed, one
positive and the other negative, the situation is handled in a fairly
H2 {clear: both;}
<H2 STYLE="clear: none;">Not Cleared!</H2>
Figure 7-78. Not clear at all
clear works by increasing the top margin of an
element so that it ends up below a floated element, so any margin
width set for the top of a cleared element should be effectively
ignored. That is, instead of being 1.5em , for
example, it could be increased to 10em , or
25px , or 7.133in , or however
You may have noticed that all of the examples in this section had
borders of exactly the same width. That's because we
didn't define a width, so it defaulted to a certain value.
Next, we'll find out about that default, and much
more.
There are four ways to assign a width to a border: you can give it a
length value such as 4px or
0.1em or use one of three
keywords. These keywords are
XML documents are easily committed to a persistence layer
XML documents may be stored in files or databases. When stored in files, XML documents are simply plain text files with tags (and possibly DTDs). It is very easy to save your XML documents to a text file and pass the text file around to other machines, platforms and programs (as long as they can understand the data). In the worst case scenario, XML documents (files) can be viewed in a text editor on just about any platform.
XML documents are also naturally committed to a database (relational or object) or any other kind of XML document store. There are commercial products available which allow you to save XML documents to an XML storage layer (which is not a database per se), like Datachannel's XStore and ODI's eXcelon. These XML store solutions are quite expensive ($10,000 to $20,000 range).
XML documents are also quite naturally retrieved from a persistence layer (databases, file systems, XML stores). This lends XML to be used in real world applications where the information being used by different parts of a system is the most important thing.
XML is platform independent, textual information
XML allows you to easily generate XML documents (that contain your information), since it is so structured.
XML parsers allow you to code faster by giving you a parser for your all your XML documents (with and without DTDs).XML documents are easily committed to a persistence layer
XML documents may be stored in files or databases. When stored in files, XML documents are simply plain text files with tags (and possibly DTDs). It is very easy to save your XML documents to a text file and pass the text file around to other machines, platforms and programs (as long as they can understand the data). In the worst case scenario, XML documents (files) can be viewed in a text editor on just about any platform.
