When an environment is left open, LaTeX gives an error at the end of the document. However it only informs about the first of them, while the rest are shown with meaningless errors:

    (\end occurred inside a group at level N)

This package replaces these errors with more useful messages which show which environments (in reverse order) were not closed. There are no user macros: just use the package.

The package is part of the bezos bundle.