From the patch notes, because I couldn't remember myself and had to go searching:
"Add tagging for mod compatibility. Mods not tagged as compatible with the latest build will be disabled at start-up as well as have a warning dialog displayed when they are enabled. This behavior can be disabled on a per-mod basis or completely in the options dialog. Mods can be tagged as compatible by either adding "<CompatibleVersions>2.0</CompatibleVersions>" to the properties section of the modinfo or by marking compatible versions in the project page of ModBuddy."

Originally posted by emperorike:

From the patch notes, because I couldn't remember myself and had to go searching:
"Add tagging for mod compatibility. Mods not tagged as compatible with the latest build will be disabled at start-up as well as have a warning dialog displayed when they are enabled. This behavior can be disabled on a per-mod basis or completely in the options dialog. Mods can be tagged as compatible by either adding "<CompatibleVersions>2.0</CompatibleVersions>" to the properties section of the modinfo or by marking compatible versions in the project page of ModBuddy."

does it matter where in the stack to put "<CompatibleVersions>2.0</CompatibleVersions>" should it be in the exact text file of each individual mod?

As to that, I've no real idea, but seems like as long as it's in that Properties section of the modinfo, shouldn't be a big deal.