the leading / denotes the start of the expression
^ anchors the regular expression to the start of the line.
$ anchors it to the end of the line.
/i means case insensitive
The regular expression basically says:
Do a case insensitive search for the start of a line being right next to the end of a line
in other words, blank entry.
if you want more info on regular expressions, see the cheat sheet here: