diff --git a/worldeditadditions_core/README.md b/worldeditadditions_core/README.md
index 0f2350c..4deee17 100644
--- a/worldeditadditions_core/README.md
+++ b/worldeditadditions_core/README.md
@@ -1,3 +1,5 @@
 # worldeditadditions_core
 
 This mod's purpose is to provide a solid base upon which the rest of WorldEditAdditions can function. Once it is complete, we will be able to mark our dependency on `worldedit` itself optional. To get to that point though will still require a significant effort in implementing enhanced versions of all existing WorldEdit commands. If you've got some free time and a great idea for a command, please do open a pull request! :D
+
+In short, `worldeditadditions_core` is a reimplementation of a number of underlying parts of the worldedit engine. Parts of `worldeditadditions_core` are likely to look very similar to parts of WorldEdit - this is because inspiration was taken from Uberi/WorldEdit when implementing `worldeditadditions_core`.
diff --git a/worldeditadditions_core/core/lib/human_size.lua b/worldeditadditions_core/core/lib/human_size.lua
new file mode 100644
index 0000000..fa8dce3
--- /dev/null
+++ b/worldeditadditions_core/core/lib/human_size.lua
@@ -0,0 +1,17 @@
+
+-- TODO: This is duplicated from worldeditadditions/utils. We should consider moving worldeditadditions/utils to worldeditadditions_core. Perhaps also we could move the definition of the worldeditadditions namespace to worldeditadditions_core too?
+
+--- Formats (usually large) numbers as human-readable strings.
+-- Ported from PHP: https://github.com/sbrl/Pepperminty-Wiki/blob/0a81c940c5803856db250b29f54658476bc81e21/core/05-functions.php#L67
+-- @param	n			number	The number to format.
+-- @param	decimals	number	The number of decimal places to show.
+-- @return	string		A formatted string that represents the given input number.
+local function human_size(n, decimals)
+	local sizes = { "", "K", "M", "G", "T", "P", "E", "Y", "Z" }
+	local factor = math.floor((#tostring(n) - 1) / 3)
+	local multiplier = 10^(decimals or 0)
+	local result = math.floor(0.5 + (n / math.pow(1000, factor)) * multiplier) / multiplier
+	return result .. sizes[factor+1]
+end
+
+return human_size
diff --git a/worldeditadditions_core/core/register_command.lua b/worldeditadditions_core/core/register_command.lua
index a503a7b..e29a1a2 100644
--- a/worldeditadditions_core/core/register_command.lua
+++ b/worldeditadditions_core/core/register_command.lua
@@ -54,7 +54,7 @@ local function register_command(cmdname, options)
 		description = options.description,
 		privs = options.privs,
 		func = function(player_name, paramtext)
-			run_command(cmdname, player_name, paramtext)
+			run_command(cmdname, options, player_name, paramtext)
 		end
 	})
 	we_c.registered_commands[cmdname] = options
diff --git a/worldeditadditions_core/core/run_command.lua b/worldeditadditions_core/core/run_command.lua
index fcd7bf1..463da39 100644
--- a/worldeditadditions_core/core/run_command.lua
+++ b/worldeditadditions_core/core/run_command.lua
@@ -1,7 +1,53 @@
+local we_c = worldeditadditions_core
 
+local human_size = dofile(we_c.modpath.."/core/lib/human_size.lua")
 
-local function run_command(cmdname, func, paramtext)
-	-- TODO: Fill this in
+-- TODO: Reimplement worldedit.player_notify(player_name, msg_text)
+
+local function run_command_stage2(player_name, func, parse_result)
+	local success, result_message = func(player_name, unpack(parse_result))
+	if result_message then
+		-- TODO: If we were unsuccessfull, then colour the message red
+		worldedit.player_notify(player_name, result_message)
+	end
+end
+
+local function run_command(cmdname, options, player_name, paramtext)
+	if options.require_pos > 0 and not worldedit.pos1[player_name] then
+		worldedit.player_notify(player_name, "Error: pos1 must be selected to use this command.")
+		return false
+	end
+	if options.require_pos > 1 and not worldedit.pos2[player_name] then
+		worldedit.player_notify(player_name, "Error: Both pos1 and pos2 must be selected (together making a region) to use this command.")
+		return false
+	end
+	
+	local parse_result = { options.parse(paramtext) }
+	local success = table.remove(parse_result, 1)
+	if not success then
+		worldedit.player_notify(player_name, parse_result[1] or "Invalid usage (no further error message was provided by the command. This is probably a bug.)")
+		return false
+	end
+	
+	if options.nodes_needed then
+		local potential_changes = options.nodes_needed(player_name, unpack(parse_result))
+		
+		local limit = we_c.safe_region_limit_default
+		if we_c.safe_region_limits[player_name] then
+			limit = we_c.safe_region_limits[player_name]
+		end
+		
+		if potential_changes > limit then
+			worldedit.player_notify(player_name, "/"..cmdname.." "..paramtext.."' may affect up to "..human_size(potential_changes).." nodes. Type //y to continue, or //n to cancel (see the //saferegion command to control when this message appears).")
+			
+			-- TODO: Wrap run_command_stage2 in safe_region stuff
+			run_command_stage2(player_name, options.func, parse_result)
+		end
+	else
+		run_command_stage2(player_name, options.func, parse_result)
+	end
+	
+	
 end
 
 return run_command
diff --git a/worldeditadditions_core/init.lua b/worldeditadditions_core/init.lua
index b34c1d6..6446338 100644
--- a/worldeditadditions_core/init.lua
+++ b/worldeditadditions_core/init.lua
@@ -15,6 +15,11 @@ local modpath = minetest.get_modpath("worldeditadditions_core")
 worldeditadditions_core = {
 	modpath = modpath,
 	registered_commands = {},
+	-- Storage for per-player node limits before safe_region kicks in.
+	-- TODO: Persist these to disk.
+	safe_region_limits = {},
+	-- The default limit for new players on the number of potential nodes changed before safe_region kicks in.
+	safe_region_limit_default = 100000,
 	register_command = dofile(modpath.."/core/register_command.lua")
 }