6.3. Handling Verboten Characters

Occasionally when dealing with XML documents, you will encounter certain characters that will cause a document to be not well formed. For example, imagine an element that contains a JavaScript function, such as the one shown in Listing 6-6. Examined from a JavaScript perspective, the function looks like it works, but when examined from an XML point of view, there is one big glaring error. Here is a hint: Look at the for loop.

Listing 6-6. A Script Element That Is Not Well Formed

<script language="JavaScript"> function hello(intTimes) { for(var i=0;i < intTimes;i++) alert('Hello, World!'); } </script>

XML interprets the less-than (<) operator as the beginning of a new element, and from an XML viewpoint, the new tag is not well formed. Fortunately, you can use one of two methods to get around this issue: entities or CDATA sections. Each of these methods is suited to a different purpose, so let's examine each to determine which better suits our problem.

6.3.1. Entities

Entities. A part of me just likes to say the word entities. It's just a fun word to say, especially to a manager who is unfamiliar with XML. Just imagine someone's reaction when being told that the XML contains entities. Talk about your flashbacks to late-night horror movies! Of course, there is always the alternative: being fitted for a jacket with wraparound sleeves. Either way, you've gotten the manager's attention.

XML has five predefined entities whose purpose it to avoid well-formedness issues when encountering select common characters. Table 6-1 defines these five entities, and later topics cover how to define additional entities.

Table 6-1. Entities

Character	Entity	Description
<	&lt;	Less than
>	&gt;	Greater than
'	&apos;	Apostrophe/single quote
"	&qout;	Double quote
&	&amp;	Ampersand

The JavaScript in Listing 6-6 can be made well formed by replacing the character < by its corresponding entity &lt;. Unfortunately, although the use of entities would correct the issue from an XML point of view, from a JavaScript perspective, there is a world of difference between < and &lt;. To make both XML and JavaScript happy, it is necessary to use a CDATA section.

6.3.2. CDATA Sections

A CDATA section is the XML equivalent of "Pay no attention to that man behind the curtain," from The Wizard of Oz. However, there is no pesky little girl with a little dog to mess things up. Because of this, XML totally ignores whatever is within a CDATA section's tags, <![CDATA[ and ]]>, as shown in Listing 6-7.

Listing 6-7. A Well-Formed Script Element

<script language="JavaScript"> <![CDATA[ function hello(intTimes) { for(var i=0;i < intTimes;i++) alert('Hello, World!'); } ]]> </script>