Can someone explain "elr" suffixes on urls?

When I blog an article from a newspaper, such as the Star Tribune piece below, the url looks like this -

h--p://www.startribune.com/local/52441552.html?elr=KArksLckD8EQDUoaEyqyP4O:DW3ckUiD3aPc:_Yyc:aUycaEacyU

All that's needed to create a valid link is the part up to and including "html." The rest is... what? Some type of tracking code?

When I try looking up "elr" on the 'net, everything I see is irrelevant (Everyone Loves Raymond, East Lancashire Railway, Endangered Language Repository, Esther Lavonne and the Rottens, Elevated Leg Rests...)

This is not important. But I'd be curious to know the answer.

Update: Per "davelog's" comment, the letters stand for "external link referral." Testing it in that regard, I went back to the paper and opened the same article via two different links at the newspaper (frontpage and "most emailed") and got two different elr suffixes, differing in the last dozen or so characters.