THe first search is for an extern tidy library, if USE_EXTERNAL_TIDY is left ON by default.
If such an 'external' tidy library is NOT found, then the source in the submodule will be used.
To use the tidy-html5 submodule, on the first clone of this repo need to use -
git submodule init
To update to the latest tidy-html5 source...
git submodule foreach git pull origin master
This did nothing: git submodule update --recursive
; eof