XML editing tools

I am new in XML editing and looking for the right approach to learn it.
I have in mind something like xmllint utility and would like to know is it capable of editing XML files or I do need something else. I would like to avoid using sed and awk, since, I think, they are not really appropriate for XML.
After looking at xmllint I feel I need to learn some commands that do manipulations of data but do not know where to start. Is it xpath I have to look at? I expect do the editing from scripts, so conventional text editor is not the option.
Please advise where to start.
Best regards
Leonid