The documentation is generated by Doxygen via the envtool.Doxyfile config-file.

Running the command doxygen envtool.Doxyfile, requires hhc.exe. This is part of the Microsoft HTML Workshop. This will generate the compressed HTML-file envtool.chm of the generated documentation.

envtool.chm can be view by the command start envtool.chm (which is normally pointing to "%WINDIR%\hh.exe"). Or loaded in the excellent KchmViewer.

But it's much easier using the GNU Makefile directly. Enter this directory and issue make or mingw32-make with one if these targets:

make all   - should produce envtool.chm in this directory.
make clean - should delete all generated files.

PS. When using the Index menu in "%WINDIR%\hh.exe", it will crash! Some issue with how I or Doxygen creates the output/index.hhk file? KchmViewer does not exhibit this bug.