Mention that the delta argument is in seconds in Node documentation

(cherry picked from commit fcb6ecaf21)

doc/classes/MainLoop.xml

@@ -113,7 +113,7 @@
 			<argument index="0" name="delta" type="float">
 			</argument>
 			<description>
-				Called each physics frame with the time since the last physics frame as argument (in seconds). Equivalent to [method Node._physics_process].
+				Called each physics frame with the time since the last physics frame as argument ([code]delta[/code], in seconds). Equivalent to [method Node._physics_process].
 				If implemented, the method must return a boolean value. [code]true[/code] ends the main loop, while [code]false[/code] lets it proceed to the next frame.
 			</description>
 		</method>

doc/classes/Node.xml

@@ -9,7 +9,7 @@
 		[b]Scene tree:[/b] The [SceneTree] contains the active tree of nodes. When a node is added to the scene tree, it receives the [constant NOTIFICATION_ENTER_TREE] notification and its [method _enter_tree] callback is triggered. Child nodes are always added [i]after[/i] their parent node, i.e. the [method _enter_tree] callback of a parent node will be triggered before its child's.
 		Once all nodes have been added in the scene tree, they receive the [constant NOTIFICATION_READY] notification and their respective [method _ready] callbacks are triggered. For groups of nodes, the [method _ready] callback is called in reverse order, starting with the children and moving up to the parent nodes.
 		This means that when adding a node to the scene tree, the following order will be used for the callbacks: [method _enter_tree] of the parent, [method _enter_tree] of the children, [method _ready] of the children and finally [method _ready] of the parent (recursively for the entire scene tree).
-		[b]Processing:[/b] Nodes can override the "process" state, so that they receive a callback on each frame requesting them to process (do something). Normal processing (callback [method _process], toggled with [method set_process]) happens as fast as possible and is dependent on the frame rate, so the processing time [i]delta[/i] is passed as an argument. Physics processing (callback [method _physics_process], toggled with [method set_physics_process]) happens a fixed number of times per second (60 by default) and is useful for code related to the physics engine.
+		[b]Processing:[/b] Nodes can override the "process" state, so that they receive a callback on each frame requesting them to process (do something). Normal processing (callback [method _process], toggled with [method set_process]) happens as fast as possible and is dependent on the frame rate, so the processing time [i]delta[/i] (in seconds) is passed as an argument. Physics processing (callback [method _physics_process], toggled with [method set_physics_process]) happens a fixed number of times per second (60 by default) and is useful for code related to the physics engine.
 		Nodes can also process input events. When present, the [method _input] function will be called for each input that the program receives. In many cases, this can be overkill (unless used for simple projects), and the [method _unhandled_input] function might be preferred; it is called when the input event was not handled by anyone else (typically, GUI [Control] nodes), ensuring that the node only receives the events that were meant for it.
 		To keep track of the scene hierarchy (especially when instancing scenes into other scenes), an "owner" can be set for the node with the [member owner] property. This keeps track of who instanced what. This is mostly useful when writing editors and tools, though.
 		Finally, when a node is freed with [method Object.free] or [method queue_free], it will also free all its children.
@@ -65,7 +65,7 @@
 			<argument index="0" name="delta" type="float">
 			</argument>
 			<description>
-				Called during the physics processing step of the main loop. Physics processing means that the frame rate is synced to the physics, i.e. the [code]delta[/code] variable should be constant.
+				Called during the physics processing step of the main loop. Physics processing means that the frame rate is synced to the physics, i.e. the [code]delta[/code] variable should be constant. [code]delta[/code] is in seconds.
 				It is only called if physics processing is enabled, which is done automatically if this method is overridden, and can be toggled with [method set_physics_process].
 				Corresponds to the [constant NOTIFICATION_PHYSICS_PROCESS] notification in [method Object._notification].
 				[b]Note:[/b] This method is only called if the node is present in the scene tree (i.e. if it's not orphan).
@@ -77,7 +77,7 @@
 			<argument index="0" name="delta" type="float">
 			</argument>
 			<description>
-				Called during the processing step of the main loop. Processing happens at every frame and as fast as possible, so the [code]delta[/code] time since the previous frame is not constant.
+				Called during the processing step of the main loop. Processing happens at every frame and as fast as possible, so the [code]delta[/code] time since the previous frame is not constant. [code]delta[/code] is in seconds.
 				It is only called if processing is enabled, which is done automatically if this method is overridden, and can be toggled with [method set_process].
 				Corresponds to the [constant NOTIFICATION_PROCESS] notification in [method Object._notification].
 				[b]Note:[/b] This method is only called if the node is present in the scene tree (i.e. if it's not orphan).
@@ -334,7 +334,7 @@
 			<return type="float">
 			</return>
 			<description>
-				Returns the time elapsed since the last physics-bound frame (see [method _physics_process]). This is always a constant value in physics processing unless the frames per second is changed via [member Engine.iterations_per_second].
+				Returns the time elapsed (in seconds) since the last physics-bound frame (see [method _physics_process]). This is always a constant value in physics processing unless the frames per second is changed via [member Engine.iterations_per_second].
 			</description>
 		</method>
 		<method name="get_position_in_parent" qualifiers="const">