`Class.PhysicsService` primarily contains methods for working with **collision
groups** which define whether a set of parts may or may not collide with parts
in other collision groups. You can register a collision group through
`Class.PhysicsService:RegisterCollisionGroup()|RegisterCollisionGroup()` and
assign parts to it by setting those parts'
`Class.BasePart.CollisionGroup|CollisionGroup` property to the **name** of the
collision group.

Creating, deleting, and modifying collision relationships between collision
groups is limited to server-side `Class.Script|Scripts`.

See
[Collision Filtering](/workspace/collisions#collision-filtering)
for usage details in Studio and within scripts.


Returns whether the specified part is in the specified collision group.
This method will throw a runtime error in the following circumstances:

- The specified group does not exist.
- The specified part is not a `Class.BasePart`.


PhysicsService:CollisionGroupContainsPart

name

The name of the collision group to check.


part

The `BasePart` to check for membership in the collision group.


`true` if the part belongs to the specified collision group, `false`
otherwise.


Returns whether the part is in the collision group.


Returns whether the two specified collision groups will collide. This
method will also return true if either of the groups are unregistered, as
the default collision mask collides with all groups.


PhysicsService:CollisionGroupsAreCollidable

name1

name2

`true` if the two groups are set to collide, `false` otherwise. Also
returns `true` if either group is unregistered.


Returns whether the two groups will collide.


Sets the collision status between two groups. This method will throw an
error if either of the groups is unregistered, so it's recommended that
you confirm each group's registration through
`Class.PhysicsService:IsCollisionGroupRegistered()` before making this
call.


PhysicsService:CollisionGroupSetCollidable

collidable

Whether the two groups should collide with each other.


Sets the collision status between two groups.


Creates a new collision group with the given name, and returns the ID of
the created group.


PhysicsService:CreateCollisionGroup

The name of the new collision group to create.


The integer ID assigned to the newly created collision group.


This method returns the ID of the collision group with the specified name.
It will throw an error if no group with the given name exists.


PhysicsService:GetCollisionGroupId

The name of the collision group being retrieved.


The ID of the retrieved collision group, or `nil` if no such group
exists.


Returns the ID of the collision group with the specified name.


Returns the name of the collision group with the corresponding ID, or an
empty string if that ID (`0`–`31`) has not been assigned to a group. The
method throws an error if the ID is outside the valid range.


PhysicsService:GetCollisionGroupName

The integer ID of the collision group to look up.


The name of the collision group with the given ID, or an empty string
if the ID has not been assigned to a group.


Returns the name of the group with the corresponding ID.


Returns a table with info on all of the place's collision groups. Each
value in the returned table is itself a table containing three members:

<table>
  <thead>
    <tr>
      <th>Member</th>
      <th>Type</th>
      <th>Description</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td>id</td>
      <td>integer</td>
      <td>The ID of the group.</td>
    </tr>
    <tr>
      <td>mask</td>
      <td>integer</td>
      <td>The collision group's mask; only for internal use.</td>
    </tr>
    <tr>
      <td>name</td>
      <td>string</td>
      <td>The name of the collision group.</td>
    </tr>
  </tbody>
</table>


PhysicsService:GetCollisionGroups

An array of tables, each containing `name` (string), `id` (integer),
and `mask` (integer) fields for a registered collision group.


Returns a table with info on all of the place's collision groups.


Returns the maximum number of collision groups the engine supports. This
value is currently 32.


PhysicsService:GetMaxCollisionGroups

The maximum number of collision groups supported, currently 32.


Returns the maximum number of collision groups.


Returns a table with info on all of the place's collision groups. Each
value in the returned table is itself a table and containing two members:

<table>
  <thead>
    <tr>
      <th>Member</th>
      <th>Type</th>
      <th>Description</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td>mask</td>
      <td>integer</td>
      <td>The collision group's mask; only for internal use.</td>
    </tr>
    <tr>
      <td>name</td>
      <td>string</td>
      <td>Name of the collision group.</td>
    </tr>
  </tbody>
</table>


PhysicsService:GetRegisteredCollisionGroups

An array of tables, each containing `name` (string) and `mask`
(integer) fields for a registered collision group.


Checks if a collision group is registered. It's recommended that you call
this method before calling methods that throw errors for unregistered
collision groups, such as
`Class.PhysicsService:CollisionGroupSetCollidable()`.


PhysicsService:IsCollisionGroupRegistered

`true` if a collision group with the given name is registered, `false`
otherwise.


Checks if a collision group is registered.


This example demonstrates one basic use of collision groups. It assigns
**BallPart** to `"CollisionGroupBall"` and **DoorPart** to
`"CollisionGroupDoor"`, then makes the two groups non-collidable using
`Class.PhysicsService:CollisionGroupSetCollidable()`.


Registers a new collision group with the given name. The name cannot be
`"Default"`.

Note that this method has a slight performance overhead based on the
number of `Class.BasePart|BaseParts` in the workspace, so it's recommended
that you register all collision groups at edit time through the Studio
[editor](/workspace/collisions#collision-groups) and call
`Class.PhysicsService:UnregisterCollisionGroup()|UnregisterCollisionGroup()`
and `Class.PhysicsService:RenameCollisionGroup()|RenameCollisionGroup()`
as infrequently as possible.


PhysicsService:RegisterCollisionGroup

The name of the collision group to register.


Registers a new collision group with the given name.


Removes the collision group with the given name. If an invalid name is
provided, this method will not do anything, although if the reserved name
`"Default"` is provided, it will throw an error. If there are any parts in
the collision group when it is removed, these parts will still maintain
the same collision group ID. The physical behavior of parts in a removed
group is undefined, so it is recommended to move any parts in a removed
group to another group. This method will throw a runtime error in the
following circumstances:

- The name `"Default"` is provided.
- The method is called from a client.


PhysicsService:RemoveCollisionGroup

The name of the collision group to remove.


Removes the collision group with the given name.


Renames the specified registered collision group, but does **not** rename
the `Class.BasePart.CollisionGroup|CollisionGroup` property of parts that
utilize the group. The first argument of this method is the name of the
group to rename, the second argument is the new name for the group. If the
specified group does not exist, this method will not do anything. The
naming conventions for the new name follow the same rules as if the group
was being created with
`Class.PhysicsService:RegisterCollisionGroup()|RegisterCollisionGroup()`.

This method will throw a runtime error in the following circumstances:

- Invalid or empty name provided for either argument.
- The method is called from a client.

Note that this method has a slight performance overhead based on the
number of `Class.BasePart|BaseParts` in the workspace, so it's recommended
that you register all collision groups at edit time through the Studio
[editor](/workspace/collisions#collision-groups) and rename
them as infrequently as possible.


PhysicsService:RenameCollisionGroup

from

The current name of the collision group to rename.


This method sets the collision group of the specified part to the group
with the specified name. It is equivalent to setting the
`Class.BasePart.CollisionGroupId`, although calling this method is the
recommended approach.

This method will throw a runtime error in the following circumstances:

- The part parameter is not a `Class.BasePart` instance.
- The specified group does not exist.


PhysicsService:SetPartCollisionGroup

The name of collision group that the part's collision group is being
set to.


Unregisters the collision group for the given name, with the following
behaviors:

- If an invalid name is provided, the method will not do anything.
- If the reserved name `"Default"` is provided **or** if the method is
  called from a client, it will throw an error.
- If there are any parts in the collision group when it is removed, those
  parts will still maintain the same collision group name. The physical
  behavior of parts in a removed group is undefined, so it's recommended
  to move any parts in a removed group to another group, such as the
  `"Default"` group.

Note that this method has a slight performance overhead based on the
number of `Class.BasePart|BaseParts` in the workspace, so it's recommended
that you register all collision groups at edit time through the Studio
[editor](/workspace/collisions#collision-groups) and call this
method as infrequently as possible.


PhysicsService:UnregisterCollisionGroup

The name of the collision group to unregister.


Unregisters the collision group for the given name.


PhysicsService

Service that provides methods for creating and managing collision groups,
which control whether sets of `Class.BasePart|BaseParts` collide with each
other.


`Instance` is the base class for all classes in the Roblox class hierarchy
which can be part of the `Class.DataModel` tree.

It is not possible to directly create root `Instance` objects, but the special
`Datatype.Instance.new()` constructor creates objects via code, taking the
name of the class as a parameter and returning the created object.


Demonstrates detecting changes to an instance's ancestry by connecting to the
`Class.Instance.AncestryChanged` event.

The ChangingPart's Parent is set to different values overtime. The parent of
the part is the part's ancestor, so the `Class.Instance.AncestryChanged` event
will fire whenever it changes.


Fires when this instance is reparented or when any of its ancestors is
reparented.

You can use this event to track the deletion of an instance in Studio,
such as manual deletion in the Explorer or through a plugin. If you need
to detect when an instance is destroyed using `Class.Instance:Destroy()`,
use the `Class.Instance.Destroying` event instead.


Instance.AncestryChanged

child

The instance whose `Class.Instance.Parent|Parent` property changed,
which can be this instance or a more distant ancestor, **not**
necessarily the instance the handler is connected to.


parent

The new parent of the `child` parameter.


Fires when the `Class.Instance.Parent` property of this object or one of
its ancestors is changed.


This event fires whenever any attribute is changed on the instance,
including when an attribute is set to `nil`. The name of the changed
attribute is passed to the connected function.

For example, the following code snippet connects the `attributeChanged()`
function to fire whenever one of the part's attributes changes:

```lua
local Workspace = game:GetService("Workspace")

local part = Workspace.Part

local function attributeChanged(attributeName)
	print(attributeName, "changed")
end

part.AttributeChanged:Connect(attributeChanged)
```

See also `Class.Instance:GetAttributeChangedSignal()` which returns an
event that fires when a specific given attribute changes.


Instance.AttributeChanged

attribute

The name of the attribute that has been changed.


Fires whenever an attribute is changed on the `Class.Instance`.


This snippet prints the names of objects as they are added to the Workspace:


Fires after an object is parented to this `Class.Instance`.

Note, when using this method on a client to detect objects created by the
server it is necessary to use `Class.Instance:WaitForChild()` when
indexing these object's descendants. This is because the object and its
descendants are not guaranteed to replicate from the server to the client
simultaneously. For example:

```
local Workspace = game:GetService("Workspace")

Workspace.ChildAdded:Connect(function(child)
	-- Use WaitForChild() since descendants may not have replicated yet
	local head = child:WaitForChild("Head")
end)
```

Note, this event only operates for immediate children of the
`Class.Instance`. For an event that captures all descendants, use
`Class.Instance.DescendantAdded`.

See also `Class.Instance.ChildRemoved`.


Instance.ChildAdded

The `Class.Instance` that has been added.


Fires after an object is parented to this `Class.Instance`.


Instance.childAdded

This snippet prints the names of objects as they are removed from the
Workspace:


Fires after a child is removed from this `Class.Instance`.

Removed refers to when an object's parent is changed from this
`Class.Instance` to something other than this `Class.Instance`. Note, this
event will also fire when a child is destroyed (using
`Class.Instance:Destroy()`) as the destroy function sets an object's
parent to `nil`.

This event only operates for immediate children of the `Class.Instance`.
For an event that captures all descendants, use
`Class.Instance.DescendantRemoving`.

See also `Class.Instance.ChildAdded`.


Instance.ChildRemoved

The `Class.Instance` that has been removed.


Fires after a child is removed from this `Class.Instance`.


This following example will print the name of any object that is added to the
Workspace:


This event fires after a descendant is added to the `Class.Instance`.

As it fires for every descendant, parenting an object to the
`Class.Instance` will fire the event for this object and all of its
descendants individually.

If you're only concerned with the **direct children** of the
`Class.Instance`, use `Class.Instance.ChildAdded` instead.

See also `Class.Instance.DescendantRemoving`.


Instance.DescendantAdded

descendant

Fires after a descendant is added to the `Class.Instance`.


The following example prints the name of any descendant as it is being removed
from the Workspace:


This event fires **immediately before** the parent `Class.Instance`
changes such that a **descendant** instance will no longer be a
descendant. `Class.Instance:Destroy()|Destroy()` changes an instance's
`Class.Instance.Parent|Parent` to `nil`, so calling that method on a
descendant of the parent will cause this event to fire.

Since this event fires **before** the descendant's removal, the parent of
the descendant will be unchanged at the time of this event firing. If the
descendant is also a **direct child** of the parent, this event will fire
before `Class.Instance.ChildRemoved`.

If a descendant has children, this event fires with the descendant first,
followed by its descendants.

#### Warning

This event fires with the descendant object that is being removed.
Attempting to set the `Class.Instance.Parent|Parent` of the descendant to
something else will fail. Below is an example that demonstrates this:

```
local Workspace = game:GetService("Workspace")

Workspace.DescendantRemoving:Connect(function(descendant)
	-- Do not manipulate the parent of the descendant in this function!
	-- This event fires BECAUSE the parent was manipulated, and the change hasn't happened yet
	-- Therefore, it is problematic to change the parent like this:
	descendant.Parent = game
end)

local part = Instance.new("Part")
part.Parent = Workspace
part.Parent = nil
```

See also `Class.Instance.DescendantAdded|DescendantAdded`.


Instance.DescendantRemoving

The `Class.Instance` that is being removed.


Fires immediately before a descendant of the `Class.Instance` is removed.


This sample demonstrates how, when using Immediate signal behavior, an
Instance being destroyed remains in place until the connected function yields.


This sample demonstrates how, when using Deferred signal behavior, an Instance
is destroyed before the signal fires.


The `Class.Instance` will never be deleted from memory while a connected
function is still using it. However, if the function yields at any point,
the `Class.Instance` and its descendants will be parented to `nil`.

If the `Class.Workspace.SignalBehavior` property is set to
`Enum.SignalBehavior.Immediate`, this event fires immediately before the
`Class.Instance` or one of its ancestors is destroyed with
`Class.Instance:Destroy()`.

If the `Class.Workspace.SignalBehavior` property is set to
`Enum.SignalBehavior.Deferred`, this event fires at the next resumption
point, which will be after the `Class.Instance` or one of its ancestors is
destroyed with `Class.Instance:Destroy()`.

With `Enum.SignalBehavior.Deferred|Deferred` behavior, connecting a script
to its own `Class.Instance.Destroying` event is problematic, as the script
will be destroyed before the callback can be called (meaning it will not
execute).

When deleting an `Class.Instance` in Studio, such as manually deleting
through the [Explorer](/studio/explorer) or through a plugin,
the `Class.Instance` isn't destroyed. Instead, the parent is set to `nil`
which you can track with `Class.Instance.AncestryChanged`.


Instance.Destroying

Fires immediately before (or is deferred until after) the instance is
destroyed via `Class.Instance:Destroy()`.


Demonstrates `Class.Instance.StyledPropertiesChanged`.


This event fires whenever any style property is changed on the instance,
including when a property is set to `nil`.


Instance.StyledPropertiesChanged

Fires whenever any style property is changed on the instance, including
when a property is set to `nil`.


This method applies a tag to the instance, with no effect if the tag is
already applied. Successfully adding a tag will fire a signal created by
`Class.CollectionService:GetInstanceAddedSignal()` with the given tag.

#### Warnings

- An instance's tags that were added client-side will be dropped if the
  server later adds or removes a tag on that instance because the server
  replicates all tags together and overwrites previous tags.

- When tagging an instance, it is common that some resources are used to
  give the tag its functionality, for example event connections or tables.
  To prevent memory leaks, it's a good idea to clean these up (disconnect,
  set to `nil`, etc.) when no longer needed for a tag. Do this when
  calling `Class.Instance:RemoveTag()`, calling
  `Class.Instance:Destroy()`, or in a function connected to a signal
  returned by `Class.CollectionService:GetInstanceRemovedSignal()`.


Instance:AddTag

The children function returns an array of the object's children.


Instance:children

Returns an array of the object's children.


This method destroys all of an instance's children and descendants.

```
local part = Instance.new("Part")

-- Add some sparkles
for i = 1, 3 do
	local sparkles = Instance.new("Sparkles")
	sparkles.Parent = part

  local sc = Instance.new("Sparkles")
  sc.Parent = sparkles
end

print("Children:", #part:GetChildren())  --> Children: 3

part:ClearAllChildren()

print("Children:", #part:GetChildren())  --> Children: 0
```

If you do not wish to destroy **all** children and descendants, use either
`Class.Instance:GetChildren()` or `Class.Instance:GetDescendants()` to
loop through those children/descendants and select what to destroy. For
example, the following code sample will destroy all
`Class.BasePart|BaseParts` descending from a `Class.Model`:

```
local Workspace = game:GetService("Workspace")

local model = Workspace:FindFirstChild("TestModel")

for _, descendant in model:GetDescendants() do
	if descendant:IsA("BasePart") then
		descendant:Destroy()
	end
end
```


Instance:ClearAllChildren

This method destroys all of an instance's children.


Demonstrates cloning a model using `Class.Instance:Clone()`.


`Clone()` creates a copy of an instance and all of its descendants,
ignoring all instances that are not
`Class.Instance.Archivable|Archivable`. The copy of the root instance is
returned by this method and its `Class.Instance.Parent|Parent` is set to
`nil`. Note that if the instance itself has
`Class.Instance.Archivable|Archivable` set to `false`, this method will
return `nil`.

If a reference property such as `Class.ObjectValue.Value` is set in a
cloned instance, the value of the copy's property depends on the
original's value:

- If a reference property refers to an instance that was **also** cloned,
  the copy will refer to the copy.
- If a reference property refers to an instance that was **not** cloned,
  the same value is maintained in the copy.


Instance:Clone

A copy of the instance, or `nil` if the instance is not
`Class.Instance.Archivable|Archivable`.


Create a copy of an instance and all its descendants, ignoring instances
that are not `Class.Instance.Archivable|Archivable`.


Instance:clone

Demonstrates destroying a Part using the `Class.Instance:Destroy()` function.

This function is the correct way to dispose of objects that are no longer
required.


Sets the `Class.Instance.Parent` property to `nil`, locks the
`Class.Instance.Parent` property, disconnects all connections, and calls
`Destroy()` on all children. This method is the correct way to dispose of
objects that are no longer required.

Disposing of unneeded objects is important, since unnecessary objects and
connections in a place use up memory which can lead to serious performance
issues over time.

As a best practice after calling `Destroy()` on an object, set any
variables referencing the object (or its descendants) to `nil`. This
prevents your code from accessing anything to do with the object.

```lua
local part = Instance.new("Part")
part.Name = "Hello, world"
part:Destroy()
-- Don't do this:
print(part.Name)  --> "Hello, world"
-- Do this to prevent the above line from working:
part = nil
```

Once an `Class.Instance` has been destroyed by this method, it cannot be
reused because the `Class.Instance.Parent` property is locked. To
**temporarily** remove an object instead of destroying it, set
`Class.Instance.Parent|Parent` to `nil`. For example:

```
local Workspace = game:GetService("Workspace")

object.Parent = nil
task.wait(2)
object.Parent = Workspace
```

To destroy an object after a set amount of time, use
`Class.Debris:AddItem()`.


Instance:Destroy

Sets the `Class.Instance.Parent` property to `nil`, locks the
`Class.Instance.Parent` property, disconnects all connections, and calls
`Destroy()` on all children.


Instance:destroy

Returns the first ancestor of the `Class.Instance` whose
`Class.Instance.Name` is equal to the given name.

This method works upwards, meaning it starts at the instance's immediate
`Class.Instance.Parent` and works up towards the `Class.DataModel`. If no
matching ancestor is found, it returns `nil`.

The following code snippet would find the first ancestor of the object
named `Car`.

```
local car = object:FindFirstAncestor("Car")
```

For variants of this method that find ancestors of a specific class,
please see `Class.Instance:FindFirstAncestorOfClass()` and
`Class.Instance:FindFirstAncestorWhichIsA()`.


Instance:FindFirstAncestor

The `Class.Instance.Name` to be looked for.


Returns the first ancestor of the `Class.Instance` whose
`Class.Instance.Name` is equal to the given name.


Returns the first ancestor of the `Class.Instance` whose
`Class.Object.ClassName` is equal to the given className.

This method works upwards, meaning it starts at the instance's immediate
`Class.Instance.Parent` and works up towards the `Class.DataModel`. If no
matching ancestor is found, it returns `nil`.

A common use of this method is finding the `Class.Model` a
`Class.BasePart` belongs to. For example:

```
local model = part:FindFirstAncestorOfClass("Model")
```

This method is a variant of `Class.Instance:FindFirstAncestor()` which
checks the `Class.Object.ClassName` property rather than
`Class.Instance.Name`. `Class.Instance:FindFirstAncestorWhichIsA()` also
exists, using the `Class.Object:IsA()` method instead to respect class
inheritance.


Instance:FindFirstAncestorOfClass

className

The `Class.Object.ClassName` to be looked for.


Returns the first ancestor of the `Class.Instance` whose
`Class.Object.ClassName` is equal to the given className.


Returns the first ancestor of the `Class.Instance` for whom
`Class.Object:IsA()` returns true for the given className.

This method works upwards, meaning it starts at the instance's immediate
`Class.Instance.Parent` and works up towards the `Class.DataModel`. If no
matching ancestor is found, it returns `nil`.

Unlike `Class.Instance:FindFirstAncestorOfClass()`, this method uses
`Class.Object:IsA()` which respects class inheritance. For example:

```
print(part:IsA("Part"))  --> true
print(part:IsA("BasePart"))  --> true
print(part:IsA("Instance"))  --> true
```

Therefore, the following code sample will return the first
`Class.BasePart` ancestor, regardless of if it is a `Class.WedgePart`,
`Class.MeshPart` or `Class.Part`.

```
local part = object:FindFirstAncestorWhichIsA("BasePart")
```

See also `Class.Instance:FindFirstAncestor()`.


Instance:FindFirstAncestorWhichIsA

Returns the first ancestor of the `Class.Instance` for whom
`Class.Object:IsA()` returns true for the given className.


The below would look in Workspace for an object name "Brick". If found, it
will change the name of the object to "Foo".


Returns the first child of the `Class.Instance` with the given name, or
`nil` if no such child exists. If the optional `recursive` argument is
`true`, this method searches all descendants rather than only the
immediate children of the `Class.Instance`.

#### Checking the Existence of an Object

`FindFirstChild()` is necessary if you need to verify an object exists
before continuing. Attempting to index a child by name using the dot
operator throws an error if the child doesn't exist.

```lua
local Workspace = game:GetService("Workspace")

-- The following line errors if the part doesn't exist in the workspace
Workspace.Part.Transparency = 0.5
```

A better approach is to use `FindFirstChild()` to first check for `Part`,
then use an `if` statement to run code that needs it.

```lua
local Workspace = game:GetService("Workspace")

local part = Workspace:FindFirstChild("Part")
if part then
	part.Transparency = 0.5
end
```

#### Finding a Child Whose Name Matches a Property

Sometimes the `Class.Instance.Name|Name` of an object is the same as that
of a property of its `Class.Instance.Parent|Parent`. When using the dot
operator, properties take precedence over children if they share a name.

In the following example, a `Class.Folder` called `Color` is added to a
`Class.Part`, which also has the `Class.Part.Color` property. Notice that
`part.Color` refers to the `Datatype.Color3` property value, not the child
`Class.Folder` instance. A benefit of using
`Class.Instance:FindFirstChild()|FindFirstChild()` is that the
introduction of new properties does not impose a risk on your code.

```lua
local part = Instance.new("Part")
local folder = Instance.new("Folder")
folder.Name = "Color"
folder.Parent = part
local c1 = part.Color  -- The property
local c2 = part:FindFirstChild("Color")  -- The child folder
```

#### Performance Notes

`Class.Instance:FindFirstChild()|FindFirstChild()` takes about 20% longer
than using the dot operator and almost 8 times longer than simply storing
a reference to an object. Therefore, you should avoid calling it in
performance-dependent code such as in tight loops or functions connected
to `Class.RunService.Heartbeat` and `Class.RunService.PreRender`. Instead,
store the result in a variable, or consider using
`Class.Instance.ChildAdded|ChildAdded` or
`Class.Instance:WaitForChild()|WaitForChild()` to detect when a child of a
given name becomes available.


Instance:FindFirstChild

The `Class.Instance.Name` to be searched for.


recursive

Whether or not the search should be conducted recursively.


Returns the first child of the `Class.Instance` found with the given name.


Instance:findFirstChild

Returns the first child of the `Class.Instance` whose
`Class.Object.ClassName|ClassName` is equal to the given `className`.
Unlike `Class.Instance:FindFirstChildWhichIsA()`, this method only returns
objects whose class matches `className`, ignoring class inheritance. If no
matching child is found, this method returns `nil`.


Instance:FindFirstChildOfClass

Returns the first child of the `Class.Instance` whose
`Class.Object.ClassName|ClassName` is equal to the given class name.


Returns the first child of the `Class.Instance` for whom
`Class.Object:IsA()` returns true for the given className.

If no matching child is found, this method returns `nil`. If the optional
recursive argument is true, this method searches all descendants rather
than only the immediate children of the `Class.Instance`.

Unlike `Class.Instance:FindFirstChildOfClass()`, this method uses
`Class.Object:IsA()` which respects class inheritance. For example:

```lua
print(part:IsA("Part")) --> true
print(part:IsA("BasePart")) --> true
print(part:IsA("Instance")) --> true
```

Therefore, the following code sample will return the first
`Class.BasePart` child, regardless of if it is a `Class.WedgePart`,
`Class.MeshPart` or `Class.Part`.

```
local part = object:FindFirstChildWhichIsA("BasePart")
```

Developers looking for a child by name, should use
`Class.Instance:FindFirstChild()` instead.


Instance:FindFirstChildWhichIsA

The `Class.Object.ClassName` to be searched for.


Returns the first child of the `Class.Instance` for whom
`Class.Object:IsA()` returns true for the given className.


Returns the first descendant found with the given `Class.Instance.Name`.

This method is disabled and cannot be used. To find the first descendant
of an instance, consider using the `recursive` parameter on
`Class.Instance:FindFirstChild()` instead.


Instance:FindFirstDescendant

The `Class.Instance.Name` to search for.


Returns the first descendant found with the given `Class.Instance.Name`.


If the `Class.Instance` is an `Class.Actor`, the `Class.Actor` itself is
returned. Otherwise, its closest ancestor `Class.Actor` is returned. If no
ancestor is an `Class.Actor`, the result is `nil`.


Instance:GetActor

Returns the `Class.Actor` associated with the Instance, if any.


This method returns the value which has been assigned to the given
attribute name. If no attribute has been assigned, `nil` is returned.

For example, the following code snippet sets and then gets the value of
the instance's `InitialPosition` attribute:

```lua
local Workspace = game:GetService("Workspace")

local part = Workspace.Part
part:SetAttribute("InitialPosition", part.Position)

local initialPosition = instance:GetAttribute("InitialPosition")
print(initialPosition)
```

#### See Also

- `Class.Instance:SetAttribute()` which sets the attribute with the given
  name to the given value.
- `Class.Instance:GetAttributes()` which returns a dictionary of key‑value
  pairs for each of the instance's attributes.


Instance:GetAttribute

The name of the attribute being retrieved.


The value which has been assigned to the given attribute name. If no
attribute has been assigned, `nil` is returned.


Returns the value which has been assigned to the given attribute name.


This method returns an event that behaves exactly like the
`Class.Object.Changed|Changed` event, except that it only fires when the
specific given attribute changes; effectively it is similar to
`Class.Object:GetPropertyChangedSignal()|GetPropertyChangedSignal()` but
for attributes.

It's generally a good idea to use this method instead of a connection to
`Class.Object.Changed|Changed` with a function that checks the attribute
name. Subsequent calls to this method on the same object with the same
attribute name return the same event.

The following code example returns a signal that fires the function
`attributeChanged()` when the part's `InitialPosition` attribute changes:

```lua
local Workspace = game:GetService("Workspace")

local part = Workspace.Part
part:SetAttribute("InitialPosition", part.Position)

local function attributeChanged()
	print("Attribute changed")
end

part:GetAttributeChangedSignal("InitialPosition"):Connect(attributeChanged)
```

See also `Class.Instance.AttributeChanged` which fires whenever any
attribute is changed on the instance.


Instance:GetAttributeChangedSignal

The name of the specified attribute for which the change signal is
being returned.


An event that fires when the given attribute changes.


Returns an event that fires when the given attribute changes.


This method returns a dictionary of key‑value pairs for each attribute
where the key is the attribute's name and the value is a non‑`nil` value.

For example, the following code snippet outputs an instance's attributes
and values:

```lua
local Workspace = game:GetService("Workspace")

local part = Workspace.Part
part:SetAttribute("InitialPosition", part.Position)
part:SetAttribute("CanUse", true)

for name, value in part:GetAttributes() do
	print(name .. " = " .. value)
end
```

See also `Class.Instance:GetAttribute()` which returns the value that has
been assigned to the given attribute name.


Instance:GetAttributes

A dictionary of string → variant pairs for each attribute where the
string is the name of the attribute and the variant is a non-nil
value.


Returns a dictionary of the instance's attributes.


The below would print the name of all objects currently in Workspace when ran.


Returns an array (a numerically indexed table) containing all of the
instance's direct children, or every `Class.Instance` whose
`Class.Instance.Parent|Parent` is equal to the object. The array can be
iterated upon using either a numeric or generic `for` loop:

```lua
local Workspace = game:GetService("Workspace")

-- Numeric loop example
local children = Workspace:GetChildren()
for i = 1, #children do
	local child = children[i]
	print(child.Name .. " is child number " .. i)
end
```

```lua
local Workspace = game:GetService("Workspace")

-- Generic loop example
local children = Workspace:GetChildren()
for i, child in children do
	print(child.Name .. " is child number " .. i)
end
```

Note that the returned array is **not** sorted in any particular order, so
manual sorting (for example using `Library.table.sort()`) is advised for
sorting the children returned by this method.

See also the `Class.Instance:GetDescendants()|GetDescendants()` method.


Instance:GetChildren

An array containing the instance's children.


Returns an array containing all of the instance's children.


Instance:getChildren

Returns a coded string of the debug ID used internally by Roblox. Note
that:

- This item is protected. Attempting to use it in a `Class.Script` or
  `Class.LocalScript` will cause an error.
- A debug ID is an ID used in debugging processes. It allows a debugger to
  read each instruction before an application processes it. All objects in
  Roblox act like processes and each run instructions (or 'code') that can
  be debugged if needed.
- This can be helpful for plugins which need to distinguish similar
  objects from one-another (such as objects that share the same name).


Instance:GetDebugId

scopeLength

Returns a coded string of the debug ID used internally by Roblox.


GetDescendants is often used to do something to all the descendants that are a
particular type of object. The code in this example uses GetDescendants and
`Class.Instance:IsA()` to find all of the parts in the workspace and turns
them green.


This object method returns an array that contains all of the descendants
of that object. Unlike `Class.Instance:GetChildren()`, which only returns
the immediate children of an object, this method finds every child of the
object, every child of those children, and so on.

Note that the returned array is **not** sorted in any particular order, so
manual sorting (for example using `Library.table.sort()`) is advised for
sorting the descendants returned by this method. Also consdier the
`Class.Instance:QueryDescendants()|QueryDescendants()` method to query
descendants by a combination of selectors and combinators.


Instance:GetDescendants

An array containing the instance's descendants.


Returns an array containing all of the descendants of the instance.


This code sample demonstrates the behavior of `Class.Instance:GetFullName()`.
It shows how the function behaves when called on an object not in the
`DataModel` hierarchy, and it also shows how the return value does not escape
special characters.


This code sample re-implements the `Class.Instance:GetFullName()` function in
Lua.


Returns a string describing the instance's ancestry. The string is a
concatenation of the `Class.Instance.Name|Name` of the object and its
ancestors, separated by periods. The `Class.DataModel` (`game`) is not
considered. For example, a `Class.Part` in the `Class.Workspace` may
return `Class.Workspace.Part`.

When called on an `Class.Instance` that is not a descendant of the
`Class.DataModel`, this method considers all ancestors up to and including
the topmost one without a `Class.Instance.Parent|Parent`.

This method is useful for logging and debugging. You shouldn't attempt to
parse the returned string for any useful operation; this method does not
escape periods (or any other symbol) in object names. In other words,
although its output often appears to be a valid Luau identifier, it is not
guaranteed.


Instance:GetFullName

Returns a string describing the instance's ancestry.


Instance

`Instance` is the base class for all classes in the Roblox class hierarchy
which can be part of the `Class.DataModel` tree.


/reference/engine/classes/PhysicsService.yaml