I work for a "major search engine" that does a lot of advertising & marketing stuff. To get the most out of it, we need customers to implement some javascript on their ecommerce sites.
As is often the case, javascript code that needs to get implemented on an ecommerce site often gets copy-pasted or emailed around a lot internally within a customer before it reaches the right person who can add it to the site's pages.
In this example somewhere along the way, a normal javascript snippet got all of the semi-colons changed from ; to ;.
In case you've not already spotted it, ; is not a ; but is actually "Greek Question Mark" (http://www.fileformat.info/info/unicode/char/037e/index.htm).
It was very confusing why Chrome was moaning about a semi-colon an illegal token. I had a genuine "Am I going mad? Seriously?" moment before I realised what was happening.