Alternate parts to the main file are present on several platforms, and have the same problems.  They are called resource forks on Mac.<p>On Windows&#x2F;NTFS they are called alternate data streams - <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Fork_(file_system)" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Fork_(file_system)</a> - to use specify a colon and name after the filename (eg example.txt:myads).<p>On Unix, Linux, OS&#x2F;2 etc you can find extended attributes - <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Extended_file_attributes" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Extended_file_attributes</a> - which allow storing key value pairs on a file.  Restrictions exist and vary.<p>As for an example of them being helpful - on Windows when you download a file from the Internet using a browser an extended attribute is used to mark that.  Trying to execute the file from Explorer then explains that it was downloaded and asks if you really want to proceed.<p>On Linux selinux can store labels in the extended attributes.<p>Older ignorant tools aren&#x27;t going to know about this, but don&#x27;t substantially harm anything.  Modern tools do know about them and do the right thing.  (eg copying a downloaded file elsewhere on Windows will still give the warning).  The Linux GNU cp command does require a --preserve xattr flag to copy extended attributes and does not do so by default.   Dropbox does support them by default and cross platform.