HFS+ is crazy
Alternate parts to the main file are present on several platforms, and have the same problems.  They are called resource forks on Mac.On Windows/NTFS they are called alternate data streams - https://en.wikipedia.org/wiki/Fork_(file_system) - to use specify a colon and name after the filename (eg example.txt:myads).On Unix, Linux, OS/2 etc you can find extended attributes - https://en.wikipedia.org/wiki/Extended_file_attributes - which allow storing key value pairs on a file.  Restrictions exist and vary.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.On Linux selinux can store labels in the extended attributes.Older ignorant tools aren't going to know about this, but don'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.