G'day filipebean,

There's a number of special characters that may need to be escaped in XML content: "<" to "&lt;"; ">" to "&gt;"; and "&" to "&amp;" (see XML Predefined Entities). So,

<rule>['^(<xyz>)']</rule>
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would become

<rule>['^(&lt;xyz&gt;)']</rule>
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Given the readability issues, it might be better to use CDATA blocks (see XML CDATA Sections) to escape the entire regex, e.g.

<rule><![CDATA[['^(<xyz>)']]]></rule>
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[Note: I haven't investigated how XML::Simple interacts with these constructs.]