davidmurdoch/jquery-placeholder — comment on commit 241d27362e57361150c503b0e0b40ab8df093b45
File: jquery.placeholder.js line 43
By mathiasbynens:

http://mothereff.in/js-variables#%E1%83%9A%5f%E0%B2%A0%E7%9B%8A%E0%B2%A0%5f%E1%83%9A It’s even valid according to ES3 / Unicode 3, so it should be safe.