While XML itself is primarily concerned with data structure rather than presentation, there are ways to handle text and indicate basic formatting within an XML document. It's crucial to remember that XML is not designed for rich text formatting like a word processor or HTML. However, you can represent text content and, to a limited extent, convey some formatting intent.

1. Text Content

• Placement: Text content appears between the start and end tags of an element.

• Example:

XML

<paragraph>This is a paragraph of text.</paragraph>

<title>My Document Title</title>

• Whitespace Handling:

• Significant Whitespace: By default, XML processors preserve all whitespace (spaces, tabs, newlines) within element content. This means that the following two examples are different:

XML

<message>Hello, world!</message>

XML

<message>

    Hello,

    world!

</message>

• xml:space Attribute: You can control whitespace handling using the xml:space attribute.

• xml:space="default": (Default behavior) Whitespace is preserved.

• xml:space="preserve": Explicitly preserves all whitespace.

• It is rarely necessary to explicitly specify. In the rare cases where an application needs to ignore extra whitespace, the application itself should handle the trimming. XML's default is to preserve it.

• Special Characters: Certain characters have special meaning in XML and must be escaped using entity references:

• < becomes &lt;

• > becomes &gt;

• & becomes &amp;

• ' becomes &apos;

• " becomes &quot;

• Example:

XML

<message>The price is &lt; $10.</message>

• CDATA Sections: If you have a large block of text containing many special characters that you don't want to escape individually, you can use a CDATA section:

XML

 <script>

    <![CDATA[

    function matchwo(a,b)

    {

    if (a < b && a < 0) then

      {

      return 1;

      }

    else

      {

      return 0;

      }

    }

    ]]>

</script>

Everything inside the <![CDATA[ ... ]]> is treated as plain text, and no escaping is needed (except for the sequence ]]>, which ends the CDATA section).

2. "Formatting" Elements (Limited)

XML doesn't have built-in elements for rich text formatting like bold, italics, headings, etc., in the way HTML does. However, you have a few options:

• Semantic Elements: You can create your own elements that imply formatting, based on their meaning. This is the preferred approach. The meaning is conveyed to the consuming application, which decides how to render.

• Example:

XML

<document>

    <chapter>

        <title>Chapter 1: Introduction</title>

        <paragraph>This is the <emphasis>first</emphasis> paragraph.</paragraph>

        <paragraph>This is the second paragraph.  It contains a <quote>short quotation.</quote></paragraph>

    </chapter>

</document>

Here, <emphasis> and <quote> don't directly specify bold or italics, but they convey the semantic meaning that these parts of the text should be emphasized or treated as a quotation. The application that processes this XML (e.g., a web browser displaying it, a document converter) would then decide how to render those elements (e.g., using <em> or <strong> in HTML, or applying specific styles).

• Using HTML within XML (with Namespaces): You can embed HTML elements within an XML document, but you must use XML namespaces to avoid conflicts. This is less common and generally discouraged for pure data representation, but can be useful in specific cases.

XML

<myDocument xmlns:html="http://www.w3.org/1999/xhtml">

  <content>

    <html:p>This is a paragraph with <html:b>bold</html:b> text.</html:p>

  </content>

</myDocument>

• The xmlns:html="http://www.w3.org/1999/xhtml" declares a namespace for HTML, allowing you to use HTML tags within your XML. The html: prefix indicates that these elements belong to the HTML namespace.

• Processing Instructions (for Stylesheets): You can link an XML document to a CSS stylesheet using a processing instruction:

XML

<?xml-stylesheet type="text/css" href="style.css"?>

<document>

    <title>My Document</title>

    <paragraph>This is a paragraph.</paragraph>

</document>

Then, in style.css, you could style the elements:

CSS

title {

    font-size: 24px;

    font-weight: bold;

}

paragraph {

    font-size: 16px;

}

This is the most common way to apply visual styling to XML when it needs to be displayed directly in a web browser. Note: browser support of direct XML+CSS rendering is limited. For complex layouts, you are much better converting the XML to HTML via XSLT.

• XSLT (Extensible Stylesheet Language Transformations): XSLT is a powerful language for transforming XML documents into other formats, including HTML. This is the recommended way to create richly formatted output from XML data. You would use XSLT to create an HTML page that displays the XML data with the desired formatting.

Key Takeaways

• XML itself is primarily about data structure and content, not presentation.

• Text content is placed between element tags.

• Special characters must be escaped or enclosed in CDATA sections.

• You can convey semantic meaning with custom element names (e.g., <emphasis>, <quote>), which can then be interpreted by applications.

• For direct display in a web browser, you can link to a CSS stylesheet or use XSLT for more complex transformations to HTML.

• For robust formatting, especially for complex documents, XSLT transformation to HTML is the best approach. This keeps the XML focused on data and the HTML/CSS focused on presentation.

In short, while XML doesn't have the built-in rich text formatting capabilities of HTML, it provides flexible ways to represent text and, through associated technologies like CSS and XSLT, allows for a wide range of presentation options.