CPAN上的XML模块可以分成三大类：对 XML 数据提供独特的接口（通常有关在XML实例和Perl数据之间的转换），实现某一标准XML API的模块，和对一些特定的XML相关任务进行简化的特殊用途模块。这个月我们先关注第一个，XML Perl专用接口。
<?xml version="1.0"?>
<camelids>
<species name="Camelus dromedarius">
<common-name>Dromedary, or Arabian Camel</common-name>
<physical-characteristics>
<mass>300 to 690 kg.</mass>
<appearance>
The dromedary camel is characterized by a long-curved
neck, deep-narrow chest, and a single hump.
...
</appearance>
</physical-characteristics>
<natural-history>
<food-habits>
The dromedary camel is an herbivore.
...
</food-habits>
<reproduction>
The dromedary camel has a lifespan of about 40-50 years
...
</reproduction>
<behavior>
With the exception of rutting males, dromedaries show
very little aggressive behavior.
...
</behavior>
<habitat>
The camels prefer desert conditions characterized by a
long dry season and a short rainy season.
...
</habitat>
</natural-history>
<conservation status="no special status">
<detail>
Since the dromedary camel is domesticated, the camel has
no special status in conservation.
</detail>
</conservation>
</species>
...
</camelids>
Bactrian Camel (Camelus bactrianus) endangered Dromedary, or Arabian Camel (Camelus dromedarius) no special status Llama (Lama glama) no special status Guanaco (Lama guanicoe) special concern Vicuna (Vicugna vicugna) endangered
Hash 如下：
my %camelid_links = (
one => { url => '
http://www.online.discovery.com/news/picture/may99/photo20.html',
description => 'Bactrian Camel in front of Great ' .
'Pyramids in Giza, Egypt.'},
two => { url => 'http://www.fotos-online.de/english/m/09/9532.htm',
description => 'Dromedary Camel illustrates the ' .
'importance of accessorizing.'},
three => { url => 'http://www.eskimo.com/~wallama/funny.htm',
description => 'Charlie - biography of a narcissistic llama.'},
four => { url => 'http://arrow.colorado.edu/travels/other/turkey.html',
description => 'A visual metaphor for the Perl5-porters ' .
'list?'},
five => { url => 'http://www.galaonline.org/pics.htm',
description => 'Many cool alpacas.'},
six => { url => 'http://www.thpf.de/suedamerikareise/galerie/vicunas.htm',
description => 'Wild Vicunas in a scenic landscape.'}
);
而我们所期望从hash中创建的文档例子为：
<?xml version="1.0">
<html>
<body>
<a href="http://www.eskimo.com/~wallama/funny.htm">Charlie -
biography of a narcissistic llama.</a>
<a href="http://www.online.discovery.com/news/picture/may99/photo20.html">Bactrian
Camel in front of Great Pyramids in Giza, Egypt.</a>
<a href="http://www.fotos-online.de/english/m/09/9532.htm">Dromedary
Camel illustrates the importance of accessorizing.</a>
<a href="http://www.galaonline.org/pics.htm">Many cool alpacas.</a>
<a href="http://arrow.colorado.edu/travels/other/turkey.html">A visual
metaphor for the Perl5-porters list?</a>
<a href="http://www.thpf.de/suedamerikareise/galerie/vicunas.htm">Wild
Vicunas in a scenic landscape.</a>
</body>
</html>
