Here is an example of the contents of a properties file:

1. a comment
   ! a comment

a = a string
b = a string with escape sequences \t \n \r
\" \' \ (space) \u0123
c = a string with a continuation line \
continuation line

Now if you put something like
key = a string with a continuation line \
continuation line
next time when you open file will see:
key = a string with a continuation line continuation line

Second:
Now "Add property" is :see pic1
why not to be: see pic2