World Flags

These flags decide about the world acting on itself, with no player behind the event at all. Each takes the Allowed field described in Region Flags, off by default. None of them accepts a variable there: no player is behind any of these events, so there is no one for a fact to key off.

Mechanical flags

Add Region Piston Modifier

Decide whether pistons may move the blocks in a region

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• Region Piston Modifier: whether a piston may move blocks inside the region.
• Region Redstone Modifier: whether redstone may power up inside the region. Powering down is always allowed, so a circuit already running when the flag goes up can still settle instead of being frozen on.
• Region Fire Spread Modifier: whether fire may spread to, and burn, blocks inside the region. This is fire arriving on its own: spreading flames, lava, lightning, an explosion, and the fireball of a ghast that nobody is answerable for. A fire a player lights, including one they throw as a fire charge, belongs to the Region Ignite Modifier instead.
• Region Fluid Flow Modifier: whether water and lava may flow into the region. The block the fluid flows into decides, so a source outside the region is stopped right at the border.
• Region Explosion Modifier: whether an explosion may break blocks inside the region. Creepers, TNT, beds in the nether, anything that explodes.

Piston and Explosion look similar and are decided differently on purpose. Region Piston Modifier cancels the whole move: a piston moves all of its blocks or none of them, so a push that touches a single protected block is stopped entirely, wherever the piston itself stands. Region Explosion Modifier instead filters the block list, taking only the protected blocks out of the explosion and leaving the rest to break. A creeper on the border of a protected town craters the field outside it and leaves the town standing, because an explosion, unlike a piston, can spare some blocks and break others in the same event.

Mob flags

Add Region Mob Spawn Modifier

Decide whether mobs may spawn in a region

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• Region Mob Spawn Modifier: whether mobs may spawn inside the region, every spawn reason counted: natural spawns, spawners, breeding, spawn eggs, and the rest. Only /summon is exempt, since that is an operator asking for a mob on purpose. The spawn location decides this, so the flag stops mobs from appearing inside the region; it does nothing to a mob that walks in from outside. Another plugin spawning an entity counts as a spawn like any other, so a region denying this silently stops whatever that plugin was trying to place there.
• Region Mob Grief Modifier: whether mobs may change blocks inside the region: endermen picking blocks up, sheep eating grass, zombies breaking doors. A player is never this flag's business, a creeper's crater is the Explosion flag's business, and a falling sand block coming to rest is the Block Place flag's.

Because none of these seven flags ever has a player behind it, none of them can apply to a region whose placement follows a variable. Limits and Gaps covers that.