The "X-support" field exists to record the value of the "support" field from an inventory system record. That's currently (2015) called the "supportClass" field in the inventory system used. It was called "Support" in the previous MFCF system.
It's used (in the MFCF version of ST) to include the support status in the description of an inventory system match. E.g. it can appear after the "machine name" field in the update and display pages.