Hi Alain,
Those warnings are probably reporting that your document has unclosed "<dt>" tags (missing "</dt>").
You might try to have Tidy add the missing "</dt>" for you with:
menu Markup > Tidy > Clean Document
After running the command and before saving the document, you can check the performed changes with:
menu Search > Find Differences… > Compare Against Disk File
and eventually revert undesired changes.
HTH
Jean Jourdain