EOL Format is end of line formatting for Unix/Linux or Windows/DOS. If you delete all blank lines in your code, and the formatting is Unix when you save, you might end up with square box characters ? ? ? to stand for the lines you’ve deleted. Which would be fine except when you upload the web page to a server and view code, you might just see several long lines of your code with those square box characters. This too would be alright, it doesn’t affect the way the web page is displayed. It just becomes a problem when you want to edit the code the next time.
The solution if you’re using Notepad++ is to select all text, choose ‘EOL Windows Format’, apply and save. When you choose Windows format instead of Unix, it restores all your nicely formatted code.