Diff for /books/www/articles/xpfe_dhtml.html between versions 1.10 and 1.17

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 <p>For a company committed to creating an application that runs on a wide range of different systems, using platform specific code was a big waste of  <p>For a company committed to creating an application that runs on a wide range of different systems, using platform specific code was a big waste of
 time. XPFE, Mozilla's cross-platform front end, was designed to solve this problem by enabling engineers to create one interface that would then work on  time. XPFE, Mozilla's cross-platform front end, was designed to solve this problem by enabling engineers to create one interface that would then work on
any operating system.  any operating system.  (In this context a front end is more than the look and feel of a Mozilla-based application, but can also include the functionality
and structure of that application.  For example, Netscape 6 does use XPFE to allow for the creation of <a
<p>This new technology started out as a time-saving technique and turned into one of Mozilla's most powerful innovations.  Mike Cornall, in an articlehref="http://www.netscape.com/themes/">different themes</a> for their browser suite, but the browser suite itself is also created using XPFE.)
about Mozilla published on LinuxToday, summarizes the history of XPFE well when he says: 'The application platform capabilities of Mozilla came about
through a happy coincidence of Open Source development, good design, and far-sighted developers who were paying attention.'<p>This new technology started out as a time-saving technique and turned into one of Mozilla's most powerful innovations.  Mike Cornall, in <a
href="http://linuxtoday.com/news_story.php3?ltsn=2000-07-25-001-07-OP-SM-0036">an article</a> published on LinuxToday, summarizes the history of XPFE
<p>When they started work on XPFE Mozilla engineers were trying to create a more efficient process that would save them time and effort, but thiswell when he says: 'The application platform capabilities of Mozilla came about through a happy coincidence of Open Source development, good design, and
technology ended up having the unintended consequence of lowering the barriers to entry for application developers.  To better understand this happyfar-sighted developers who were paying attention.'
coincidence and why it can be so useful for developers it is necessary to take a closer look at what XPFE is made of.
<p>Mozilla engineers were trying to create a more efficient process that would save them time and effort, but this technology ended up having the
<hr>unintended consequence of lowering the barriers to entry to application development.  To better understand this happy coincidence and why it can be so
 useful for developers it is necessary to take a closer look at what XPFE is made of.
   
 <p><b>Understanding XPFE</b>  <p><b>Understanding XPFE</b>
   
<p>The technologies that XPFE uses are all existing Web standards, such as Cascading Style Sheets, JavaScript and XML (the XML component is a new<p>The technologies that XPFE uses are all existing Web standards, such as <a href="http://www.w3.org/Style/CSS/">Cascading Style Sheets</a>, 
language called XUL, the XML-based User Interface Language).  Since well understood Web standards are being used to create applications instead of<a href="http://www.ecma.ch/ecma1/STAND/ECMA-262.HTM">JavaScript</a> and <a href="http://www.w3.org/XML/">XML</a> (the XML component is a new
platform-specific C code, a whole new group of people now have the ability to create their own applications using Mozilla.language called XUL, the XML-based User Interface Language).  In it's most simple form, XPFE can be thought of as simply the union of each of these 
standards.
<p>In the sense that XPFE uses some of the same standards that are used to create Web pages, Mozilla-based applications can even be thought of as Web 
pages.  Gecko, the HTML rendering engine that Mozilla uses, also draws all XPFE content, so a Web page and an application created with XPFE are on one 
level treated the same way by Mozilla itself. 
 
<p>Web developers and designers who use Mozilla are naturally attracted to the fact that they can create applications using the same skills and 
techniques that they used to create Web pages in the past.  The specifics involved with creating Mozilla applications are different but should seem very 
familiar to anyone who has created for the Web before. 
 
<p>When talking about front ends it is important to clarify what this means.  In this context a front end is more than the look and feel of a 
Mozilla-based application, but includes the functionality and structure of that application as well.  More simply put, XPFE allows users to do more than 
just create a skin for an application.  For example, Netscape 6 does use this functionality to allow for the creation of <a 
href="http://www.netscape.com/themes/">different themes</a> for their browser suite, but the browser suite itself is also created out of these same 
technologies. 
   
 <center>  <center>
 <p><img src="http://books.mozdev.org/screenshots/moz_0101.gif"><br>  <p><img src="http://books.mozdev.org/screenshots/moz_0101.gif"><br>
 <font size="-1"><i>Figure 1: XPFE Framework</i></font>  <font size="-1"><i>Figure 1: XPFE Framework</i></font>
 </center>  </center>
   
<p>To understand all of the capabilities of XPFE, we can look at how the different components of it fit together.  JavaScript is used to create the<p>To understand how XPFE works, we can look at how the different components of it fit together.  JavaScript is used to create the functionality for a
functionality for a Mozilla-based application, Cascading Style Sheets are used for formatting the look and feel, and XUL is used for creating theMozilla-based application, Cascading Style Sheets are used for formatting the look and feel, and XUL is used for creating the application's structure.  
application's structure.  Viewed together these three standards can be seen forming the triangle in Figure 1 above.Viewed together these three standards can be seen forming XPFE in Figure 1 above.
 
 <p>Instead of using platform-specific C code to create an application, XPFE uses these well understood Web standards that are by design inherently
 platform independent.  Since the framework of XPFE is inherently platform independent, so are the applications that are created with it.  Since the
 framework is also made up of tools that are used to create Web pages, anyone familiar with creating a Web page can use XPFE to create a cross-platform
 application.
 
 <p>Although the actual creation of Mozilla-based applications can be much more complicated than building a Web page, XPFE allows developers to create
 applications in the same way they would create a Web page.  Or to put it another way, the application is now a Web page.  Gecko, the rendering engine
 that Mozilla uses to draw a Web page in the browser, even draws the Mozilla application on the desktop.
   
 <p><b>Comparing XPFE and DHTML</b>  <p><b>Comparing XPFE and DHTML</b>
   
Line 63  and CSS that allows a developer to creat Line 60  and CSS that allows a developer to creat
 this idea by allowing the creation of applications that are more powerful, more flexible and that can live outside of the browser window as stand-alone  this idea by allowing the creation of applications that are more powerful, more flexible and that can live outside of the browser window as stand-alone
 programs.  programs.
   
<p>Figure 2 below illustrates the similarities between XPFE and DHTML.  Both use JavaScript to create functionality, both use CSS to format the design<p>Figure 2 below illustrates the similarities between XPFE and DHTML.  Both use JavaScript to create functionality, both use CSS to format design and
and layout, and both use a fairly simple mark-up language to describe content.  The difference between the two is that one of these mark-up languages islayout, and both use a fairly simple mark-up language to describe content.  The difference between the two is that one of these mark-up languages is HTML
HTML and the other is XUL.and the other is XUL.
   
 <center>  <center>
 <p><img src="http://books.mozdev.org/screenshots/moz_0102.gif"><br>  <p><img src="http://books.mozdev.org/screenshots/moz_0102.gif"><br>
Line 77  link together separate text documents on Line 74  link together separate text documents on
 can't make it an appropriate language to use for developing applications.  XUL is a language specifically designed for creating user interfaces, so it  can't make it an appropriate language to use for developing applications.  XUL is a language specifically designed for creating user interfaces, so it
 makes sense that XPFE is more suited for application development than DHTML.  makes sense that XPFE is more suited for application development than DHTML.
   
<p>Fortunately since XUL as a language is structurally similar to HTML it is simple enough to learn if you are already familiar with the basic language<p>Since XUL is structurally similar to HTML, knowledge of building Web pages will give you a boost in learning how to create cross-platform
of the Web.  Even if you have never used HTML before, XUL uses a straight-forward <a href="http://www.mozilla.org/xpfe/xulref/">collection of tags</a>Mozilla-based applications.  Even if you have never used HTML before, XUL uses a straight-forward <a
that makes it easy to get comfortable with it in a short time.  Once you become accustomed to using XUL you will be ready to start using XPFE to createhref="http://www.mozilla.org/xpfe/xulref/">collection of tags</a> that makes it easy to get comfortable with it in a short time.  Once you become
your own applications.accustomed to using XUL you will be ready to start using XPFE to create your own applications.
<p><b>Oversimplifying in the Metaphor</b><p><b>Oversimplifying Things</b>
<p>This overview of XPFE as a simple evolution of DHTML is an oversimplification of the story and deliberately leaves out much important information.  <p>Describing XPFE as a more sophisticated version of DHTML is an oversimplification and deliberately leaves out much important information.  These
These details were ignored at first to give a conceptual framework for understanding the new ideas that XPFE represent.  Now that we've gotten past thedetails were ignored in the comparison to give a better understanding of the basic framework of XPFE.  Now that we've gotten past the basics, we can go
basics, we can go back and talk about the rest of the functionality available with using Mozilla to create applications.back and talk about the rest of the functionality available with Mozilla that makes it such a powerful framework for creating applications.
   
 <p>At the <a href="http://meetzilla.mozdev.org/second_meeting.html">Second Mozilla Developer Meeting</a>, Rob Ginda, the creator of ChatZilla, lead a  <p>At the <a href="http://meetzilla.mozdev.org/second_meeting.html">Second Mozilla Developer Meeting</a>, Rob Ginda, the creator of ChatZilla, lead a
 discussion group about Mozilla as Platform.  In this session he listed all of the following as components of a Mozilla-based application:  discussion group about Mozilla as Platform.  In this session he listed all of the following as components of a Mozilla-based application:
   
 <FONT COLOR="#800000">  
 <UL>  <UL>
 <LI>XUL (XML-based User Interface Language) - Used to create the structure and content of an application.<br><br>  <LI>XUL (XML-based User Interface Language) - Used to create the structure and content of an application.<br><br>
 <LI>CSS (Cascading Style Sheets) - Used to create the look and feel of an application.<br><br>  <LI>CSS (Cascading Style Sheets) - Used to create the look and feel of an application.<br><br>
<LI>JavaScript - Used to create the functionality of an application.<br><br><LI>JavaScript - Used to create the functionality of an application. (Other scripting languages, such as Python, Perl or Ruby, can be used in 
 place of Javascript to create functionality for an application.)<br><br>
 <LI>XPInstall (Cross-Platform Install) - Used to package applications so that they can be installed on any platform.<br><br>  <LI>XPInstall (Cross-Platform Install) - Used to package applications so that they can be installed on any platform.<br><br>
<LI>RDF (Resource Description Framework) - Used to store data and transmit information.  Generally regarded to be one of the most complicated aspects of XPFE.<br><br><LI>RDF (Resource Description Framework) - Used to store data and transmit information.  Generally regarded to be one of the most complicated 
<LI>DTD (Document Type Definition) - Used for localization and internationalization, more commonly referred to in short-hand as L12N and I18N respectively.<br><br>aspects of XPFE.<br><br>
 <LI>DTD (Document Type Definition) - Used for localization and internationalization, more commonly referred to in short-hand as L12N and I18N 
 respectively.<br><br>
 <LI>XBL (eXtensible Binding Language) - Used to create reusable widgets using a combination of XUL and JavaScript.<br><br>  <LI>XBL (eXtensible Binding Language) - Used to create reusable widgets using a combination of XUL and JavaScript.<br><br>
 <LI>XUL templates - Used to create a framework for importing data into an application with a combination of RDF and XUL.<br><br>  <LI>XUL templates - Used to create a framework for importing data into an application with a combination of RDF and XUL.<br><br>
 <LI>XPCOM/XPConnect - Used to allow JavaScript, or potentially any other scripting language, to access and utilize C and C++ libraries.  <LI>XPCOM/XPConnect - Used to allow JavaScript, or potentially any other scripting language, to access and utilize C and C++ libraries.
 </UL>  </UL>
 </FONT>  
   
 <p>Each of these technologies is important and several of these deserve to have whole books devoted to them.  Although each of these technologies is  <p>Each of these technologies is important and several of these deserve to have whole books devoted to them.  Although each of these technologies is
 important there is a distinction to be made among them.  Some of these are essential to the creation of a Mozilla application and some of them provide  important there is a distinction to be made among them.  Some of these are essential to the creation of a Mozilla application and some of them provide
 powerful extra features that can be used in addition to the basic functionality.  powerful extra features that can be used in addition to the basic functionality.
   
 <p>For example, <a href="http://www.mozilla.org/rdf/doc/">RDF</a> is an extremely powerful technology for using data in Mozilla but it is possible to  <p>For example, <a href="http://www.mozilla.org/rdf/doc/">RDF</a> is an extremely powerful technology for using data in Mozilla but it is possible to
create an application without using it.  <a href="http://www.mozilla.org/projects/l10n/mlp.html">Localization</a> also provides Mozilla with a greatcreate an application without it.  <a href="http://www.mozilla.org/projects/l10n/mlp.html">Localization</a> also provides Mozilla with a great amount of
amount of flexibility and usability but there are many existing applications that don't take advantage of this feature.  It wouldn't be possible toflexibility but there are many existing applications that don't take advantage of this feature.  It wouldn't be possible to create an application without
create an application without XUL though.XUL though.
 
 <hr>
   
 <p><b>Judge For Yourself</b>  <p><b>Judge For Yourself</b>
   
Line 126  ActiveState's <a href="http://www.active Line 126  ActiveState's <a href="http://www.active
 href="http://www.hacksrus.com/~ginda/chatzilla/">ChatZilla</a> IRC client, and Zope's <a href="http://www.zope.org/Resources/Mozilla/">Mozilla  href="http://www.hacksrus.com/~ginda/chatzilla/">ChatZilla</a> IRC client, and Zope's <a href="http://www.zope.org/Resources/Mozilla/">Mozilla
 Initiative</a>.  Initiative</a>.
   
   <br><br>
   
   <p><i>Thanks to Julia Kleyman for creating the illustrations used in this article.</i>
   
 </body>  </body>
 </html>  </html>
   

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