This isn’t actually for SharePoint though.
When Microsoft Office saves file as HTML, it puts all real files under xxx_files. More on here: https://sharemypoint.wordpress.com/tag/_files/
When you try to rename/move/delete the root file, the associated _files folder will be changed accordingly. The key is in this line in the root file
<link rel=File-List href=”[your file name]_files/filelist.xml”>
If this line is removed, Windows Explorer will give you a warning only and won’t automatically move the _files folder.
This trick is useful for me when I need to rename the HTML root file. Otherwise, SharePoint will give you error message saying you can not rename the “thick” file (_file folder).