You can edit XML- or plt-files with standard text editors like wordpad.
This is true, thankfully wordpad also understand XML, otherwise, it has some quirky save time habits that make it frustrating to use.
I have found it easier that to use editors that provide at basic syntax highlighting, especially for whatever extension happen to be working with. This helps with just trying to do something at a glance on the fly. There are a lot of them that are free (quite a few of them are open source as well if that is a concern). This also depends on how nitty gritty you are going to with text editing and how much you are going to spend in a text editor looking at them. I'm in a text editor all the time, so basic syntax highlighting does help especially if editing code/markup that wasn't created/generated by myself, but I'm just editing it on the fly.