Learning Java, 4th Edition

XML Basics

The basic syntax of XML is extremely simple. If you’ve worked with HTML, you’re already halfway there. As with HTML, XML represents information as text using tags to add structure. A tag begins with a name sandwiched between less than (<) and greater than (>) characters. Unlike HTML, XML tags must always be balanced; in other words, an opening tag must always be followed by a closing tag. A closing tag looks just like the opening tag but starts with a less than sign and a slash (</). An opening tag, closing tag, and any content in between are collectively referred to as an element of the XML document. Elements can contain other elements, but they must be properly nested (all tags started within an element must be closed before the element itself is closed). Elements can also contain plain text or a mixture of elements and text (called mixed content). Comments are enclosed between <!— and —> markers. Here are a few examples:

<!-- Simple -->
<Sentence>This is text.</Sentence>

<!-- Element -->
<Paragraph><Sentence>This is text.</Sentence></Paragraph>

<!-- Mixed -->
<Paragraph>
        <Sentence>This <verb>is</verb> text.</Sentence>
</Paragraph>

<!-- Empty -->
<PageBreak></PageBreak>

An empty tag can be written more compactly in a special form using a single tag ending with a slash and a greater-than sign (/>):

<PageBreak/>

Attributes

An XML element can contain attributes, which are simple name-value pairs supplied inside the start tag.

<Document type="LEGAL"id="42">...</Document>
<