Limits and Gaps

Flags resolve against a player wherever they can, and a few of them cannot always find one. This page collects where a flag abstains, and what no flag sees at all.

Flags with no player behind them

Region Piston Modifier, Region Redstone Modifier, Region Fire Spread Modifier, Region Fluid Flow Modifier, Region Explosion Modifier, Region Mob Spawn Modifier, and Region Mob Grief Modifier all decide about events with no player behind them. That has one consequence worth knowing: none of these seven flags can apply to a region whose placement follows a variable.

A variable placement region only exists per viewer. Typewriter resolves where it is by asking for a specific player, and without a player there is nothing to resolve against. The seven flags above never have one to ask.

Most of the remaining flags have a player behind them nearly always, and behind some of their events never. Region Block Place Modifier also decides about crops growing and vines spreading, Region Block Break Modifier about ice melting and leaves decaying, Region Block Interact Modifier about a hopper pulling from a locked chest, and Region Bucket Modifier, Region Ignite Modifier, Region Trample Modifier and Region Entity Damage Modifier each about a dispenser or a mob doing the same thing a player would. On a variable placement region those cases have no player to resolve with, so the flag applies to what players do and not to the rest.

There is a third case, and it is the one that catches people out. Binding a flag's own Allowed field to a variable, rather than the region's placement, has the same problem from the other side: a fact needs a player to read, and a crop growing has none. Such a flag abstains for those events and whatever region sits below it decides instead. So a farm region whose Allowed reads "is a member" does not stop its own wheat from growing, and does not protect it either; put a second region under it with a constant Allowed if the world's own changes need a rule too.

None of the three throws an error, and none of them fails silently either. Typewriter logs a console warning naming the region and the flag, once at startup and again on every reload, so you find out instead of wondering why the flag never seems to apply. Give the region a constant placement, or the flag a constant Allowed, or accept the gap the warning describes.

What the flags do not cover

A few things still happen inside a region that no flag sees, and it is better to know the edges than to discover them:

• Damage nobody dealt directly. Region Pvp Modifier covers what a player did, including their TNT, their lingering potion and their pet. It cannot cover a player setting you on fire and walking away, or shoving you into lava: those land later as fire or fall damage with nobody attached, and only Region Player Damage Modifier sees them.
• What an explosion takes that is not a block. Region Explosion Modifier filters the block list, so a creeper proof town keeps its walls and still loses the item frames, paintings and armour stands hanging on them. Carry Region Entity Damage Modifier as well when the decoration matters.
• A region boundary that cuts through a player. The block flags decide on the block's own center, so a block is inside or outside and nothing in between. The combat flags decide on the victim's feet, while region membership (events, audiences, displays) counts a player as inside as soon as any part of them overlaps. A player leaning over the boundary can be a member of the region and still stand outside it as far as the combat flags are concerned. Keep protected areas a block or two larger than the thing they protect and the difference never comes up.

When a flag does not do what you expected somewhere, /tw region flags reports which region decided it there.