It allows the player to take the Discretionary Action Hide. 1. Hide is not a subset of Play. 2. Hiding a card does not open a chain. 3. Playing a card from facedown (or "from Hidden") does open a chain.
§ 811.1.c Core Rules PDF (officieel)
§ 811 Hidden
§ 811.1 Hidden is a keyword that acts as a prerequisite to perform the Hide Discretionary Action.
