I'm having a hard time figuring out How to use HTMLRewritter. I have an XML-like structure, small snippets, like so: ```xml <y> <a>xxx</a> <b>xxx</b> <c>xxx</c> </y> ``` I want to transform it like so: ```xml <y> <s> <a>xxx</a> <b>xxx</b> </s> <c>xxx</c> </y> ``` Any ideas?