In the Prolog of a book it explains the target of commentaries that appear along with the exercices:
"The target of the commentary is to make clear to the student the difference between his mother tongue and this he is studiying.
Комментарии снабжены схемами и таблицами, которые наглядно представляют те или иные особенности русской фонетики."
General sense of the phrase is clear but I would prefer a rather precise. The problem is how link "commentaries" with "supplies". Tks.