According to the XML manual: << 2.1 >> TEX versus LUA It will not come as a surprise that we can access xml files from TEX as well as from Lua. In fact there are two methods to deal with xml in Lua. First there are the low level xml functions in the xml namespace. On top of those functions there is a set of functions in the lxml namespace that deals with xml in a more TEXie way. << 3.7 >> manipulation You can use Lua code to manipulate the tree and it makes no sense to duplicate this in TEX. In the future we might provide an interface to some of this functionality. Keep in mind that manipuating the tree might have side effects as we maintain several indices into the tree that also needs to be updated then. Having read that, I was loooking for the documentation of the commands that are available in the xml namespace. I want to manipulate a XML tree in LMTX lua. But looking online gives me all kinds of different XML-solutions that are proposed for lua. Which one is embedded in LMTX and available in the xml namespace? But then I get confused because other elements like xml.first, xml.collected are in the xml namespavce and mentioned. So, maybe I misunderstand things and is the documentation in << 5.5 >> selectors and injectors This section describes a bit special feature, one that we needed for a project where we could not touch the original content but could add specific sections for our own purpose. Hopefully the example demonstrates its useability. But that part I do not understand. What I need (in LMTX lua) to add (sub)nodes to the XML node (that I read with xml.first()) because the data I get is broken and I need to fix it before I can use it (and I cannot get good data) The easiest way is to add the correct data to the XML and then use it in my code. If I cannot do that I need to write parallel code that largely does the same as what I already have (ugh).. G