Inserting and deleting XML nodes and elements using Nokogiri

I want to extract parts of an XML file and make a note that I extracted some part in that file, like "here something was extracted".

I'm trying to do this with Nokogiri, but it seems to not really be documented on how to:

1. delete all childs of a <Nokogiri::XML::Element>
2. change the inner_text of that complete element

Any clues?