In SUD, the mod relation is used for all modifiers (as opposed to UD set of label amod, advmod…).
Hint
Most of the times, mod is used without extension.
Frequent extensions are:
mod@relcl
Other extensions appear during conversion from UD ⇒ SUD, UD subrelation are kept as “deep” SUD relation for information preserving.
For instance, UD:nmod:tmod ⇒ SUD:mod@tmod.