A handle for a [Resource]'s unique identifier. The RID [Variant] type is used to access a low-level resource by its unique ID. RIDs are opaque, which means they do not grant access to the resource by themselves. They are used by the low-level server classes, such as [DisplayServer], [RenderingServer], [TextServer], etc. A low-level resource may correspond to a high-level [Resource], such as [Texture] or [Mesh]. [b]Note:[/b] RIDs are only useful during the current session. It won't correspond to a similar resource if sent over a network, or loaded from a file at a later time. Constructs an empty [RID] with the invalid ID [code]0[/code]. Constructs a [RID] as a copy of the given [RID]. Returns the ID of the referenced low-level resource. Returns [code]true[/code] if the [RID] is not [code]0[/code]. Returns [code]true[/code] if the [RID]s are not equal. Returns [code]true[/code] if the [RID]'s ID is less than [param right]'s ID. Returns [code]true[/code] if the [RID]'s ID is less than or equal to [param right]'s ID. Returns [code]true[/code] if both [RID]s are equal, which means they both refer to the same low-level resource. Returns [code]true[/code] if the [RID]'s ID is greater than [param right]'s ID. Returns [code]true[/code] if the [RID]'s ID is greater than or equal to [param right]'s ID.