CODE - What is the meaning of S3 XT? (Special Crossing T3), page-8

Hi Gents

I just had a large S3 XT go through for OBL one of my holdings..

I also had an SP XT go through on Tuesday for WGO..

Does anyone know what an SP XT means?
It was circa 1% of shares on issue (12m shares) and took place at a discount to the market price.