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This tutorial lesson is part of a series dedicated to learning XML.
I recommend that you open another copy of this document in a separate browser window and use the following links to easily find and view the figures and listings whileyou are reading about them.
I recommend that you also study the other lessons in my extensive collection of online programmingtutorials. You will find a consolidated index at www.DickBaldwin.com .
XML can be used to produce a variety of applications. Flex is an XML application developed by Adobe that can be used to produce code that will run inthe Adobe Flash player.
Listing 1 shows the code from a very simple Flex MXML file. (Note that the code shown in Listing 1 is from Flex version 3.x. Code from version 4.xwould be different in several respects.)
| Listing 1 . Simple Flex MXML code. |
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<?xml version="1.0" encoding="utf-8"?><!--DragAndDrop04--><mx:Application
xmlns:mx="http://www.adobe.com/2006/mxml"xmlns:cc="CustomClasses.*"><cc:Driver/></mx:Application> |
I'm not going to explain the MXML code in this lesson. I am simply providing thecode as an example of an XML document so you can see what a real XML document looks like.
What is a tag?
I will refer to items enclosed in angle brackets, such as those shown in Figure 1, as tags.
| Figure 1 . Tag example. |
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<book>...</book> |
The first tag shown in Figure 1 is often referred to as a start tag or an opening tag . The second tag is often referred to as an end tag or a closing tag .
Note that the start tag and the end tag differ only in that the end tag contains a slash character. However, the start tag can also contain optionalnamespace indicators and attributes as discussed below.
What are elements, content, and attributes?
Listing 2 contains a start tag and an end tag with an attribute and some content .
| Listing 2 . An element containing tags, content, and an attribute. |
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<chap number="1">Text for Chapter 1</chap> |
An element
The entire set of characters beginning with the start tag and ending with the end tag constitutes an element .
An element usually consists of a start tag and an end tag with the content sandwiched in between the two tags, but there are exceptions to that rule. Youwill learn about those exceptions, including empty elements later.
The tags
You have probably already recognized the tags in Listing 2 as the two sets of characters beginning with a left angle bracket and ending with a right anglebracket.
The start tag may contain optional attributes. In Listing 2, a single attribute provides the number value for the chapter.
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