Zone

Client-sided Zone example:

local ReplicatedStorage = game:GetService("ReplicatedStorage")
local HitboxRemaster = require(modules:WaitForChild("HitboxRemaster"))
local QueryFunction = ReplicatedStorage:WaitForChild("QueryFunction")
local partList = workspace.ZoneTest:GetChildren() -- All members of partList MUST be BasePart!

local Zone = HitboxRemaster.newZone({
    ["CharacterResolution"] = "OnePart",
    ["QueryType"] = "Full"
})
Zone:AddMemberBulk(partList)

Zone.PartEntered:Connect(function(part)
    print("Part entered! " .. part.Name)
end)

Zone.PartLeft:Connect(function(part)
    print("Part left! " .. part.Name)
end)

Zone.CharacterEntered:Connect(function(char)
    print("Character entered! " .. char.Name)
end)

Zone.CharacterLeft:Connect(function(char)
    print("Character left! " .. char.Name)
end)

Zone.PlayerEntered:Connect(function(char)
    print("Player entered! " .. char.Name)
end)

Zone.PlayerLeft:Connect(function(char)
    print("Player left! " .. char.Name)
end)

Zone:Activate()

QueryEvent.OnClientInvoke = function()
    return Zone:GetCharactersInside()
end

Note: Zone can be used the same way in both server and client.