Seems like it's being appended to video links shown on youtube that are not from either search results or related videos. I suspect this is a way for them to e

Seems like it's being appended to video links shown on youtube that are not from either search results or related videos. I suspect this is a way for them to exclude click metrics, etc. from videos that were not shown as a result of machine learning/lexical analysis/whatever. I'm sure they've been identifying how videos propagate since forever, but my guess is that they recently decided it would be efficient to add some cryptic-looking parameter (that probably just corresponds to a boolean) to all video links shown on channels, the home page, etc.