It appears that TeXStudio has a built-in DIFF feature. For example, one can define the syntax highlighting used for differences in the options dialogue.
But if I have two files to compare, say article.tex and article_old.tex, how do I launch the DIFF mode?
The only way I found is to open article.tex and then use "Show differences between two files" item under "File -> SVN..." and then select "article_old.tex". But this behaves very strangely, for example it only hightlights things that are present in article.tex and not in article_old.tex, but not vice versa. (This seems to be the case simply because only lines that are contained in the currently open file are highlighted, and when more lines are present in the OTHER file, they cannot be hightlighted in the currently open one, simply because they are not there.)
The option "Show differences between two files (relative to original file)" behaves even less comprehensibly.
I was unable to find any documentation of the DIFF feature online, so I am asking here: What do I need to do to just get "normal" DIFF between two files, as one would expect?