The <apply-filter> action allows all the text content beneath an element to be run through a filter. The filter is specified in Perl5 substitute syntax as the value of the rule attribute.
Example 1: The following rule uppercases every word in the text content beneath an <s> element in the target document:
<self>
<element name="s"/>
<apply-filter rule="s/(\w+)/\u$1/g"/>
</self>