user: How do I use Header in Blender? Include parameters, examples, warnings and best practices.

assistant: ### View Menu

Sidebar `N`
:   Shows or hides the [Sidebar Region](../../interface/window_system/regions.xhtml#ui-region-sidebar).

Adjust Last Operation
:   Displays a pop-up panel to alter properties of the last
    completed operation. See [Adjust Last Operation](../../interface/undo_redo.xhtml#bpy-ops-screen-redo-last).

Channels
:   Shows or hides the Track Region.

Playback Controls
:   Show or hide the [Playback Controls](../../animation/animation_editors.xhtml#animation-editors-footer).

---

Frame Selected `NumpadPeriod`
:   Pans and zooms the view to focus on the selected strips.

Frame All `Home`
:   Pans and zooms the view to show all strips.

Frame Scene/Preview Range
:   Reset the horizontal view to the current scene frame range,
    taking the preview range into account if it is active.

Go to Current Frame `Numpad0`
:   Centers the view on the Playhead.

---

Realtime Updates
:   Whether to update other views (such as the 3D Viewport) while you’re moving strips around.
    If disabled, the other views only get updated once you finish the move.

Show Control F-Curves
:   Shows a graph on top of each strip that uses [Animated Influence](sidebar.xhtml#bpy-types-nlastrip-influence).

---

Show Markers
:   Shows the marker region (provided any markers have been defined).
    When disabled, the [Marker Menu](#marker-menu) is also hidden and marker operators are not available in this editor.

Show Local Markers
:   Shows action-local markers (which you can create in the [Action Editor](../dope_sheet/editing.xhtml#dopesheet-marker-menu)).
    This can be useful to align strips to each other.

    [image reference removed]

    Local markers shown in the NLA Editor (top) and the Action Editor (bottom).

Use Timecode `Ctrl`-`T`
:   Shows timing in seconds instead of frames.

Sync Visible Range
:   Synchronizes the horizontal panning and scale of the editor
    with other time-based editors that also have this option enabled.
    That way, they always show the same section of time.

---

Set Preview Range `P`
:   Lets you drag a box to define a time range for previewing. As long as this range is active,
    playback will be limited to it, letting you repeatedly view a segment of the animation without
    having to manually rewind each time.

    You can change the start or end frame using the corresponding button in the
    Timeline editor’s [Playback](../../animation/animation_editors.xhtml#animation-editors-playback) popover.
    Alternatively, you can simply run *Set Preview Range* again.

Clear Preview Range `Alt`-`P`
:   Clears the preview range.

Set Preview Range to Selected `Ctrl`-`Alt`-`P`
:   Applies a preview range that encompasses the selected strips.

---

Area
:   Area controls. See the [user interface](../../interface/window_system/areas.xhtml)
    documentation for more information.

### Select Menu

All `A`
:   Selects all strips.

None `Alt`-`A`
:   Deselects all strips.

Invert `Ctrl`-`I`
:   Inverts the current selection.

---

[Box Select](../../interface/selecting.xhtml#bpy-ops-select-box) `B`
:   Lets you drag a box and selects the strips that are partially or completely inside it.

Box Select (Axis Range) `Alt`-`B`
:   Lets you drag a box and selects the strips that overlap the corresponding time range,
    even if they’re above or below the box.

---

Before Current Frame `[`
:   Selects all the strips that start before (or on) the current frame.

After Current Frame `]`
:   Selects all the strips that end after (or on) the current frame.

### Marker Menu

[Markers](../../animation/markers.xhtml) are used to denote frames with key points or significant events
within an animation. Like with most animation editors, they’re shown at the bottom.

[image reference removed]

Markers in animation editor.

For descriptions of the different marker tools, see [Editing Markers](../../animation/markers.xhtml#animation-markers-editing).

### Add Menu

Action `Shift`-`A`
:   Adds a strip referencing an action to the active track.

Transition `Shift`-`T`
:   Adds a transition strip between the two selected action strips.

Sound `Shift`-`K`
:   Adds a strip that controls when the [Speaker Objects](../../render/output/audio/speaker.xhtml) object plays its sound clip.

---

Selected Objects
:   Makes the selected objects appear in the NLA Editor without adding an action or track to them.

See [Strips](strips.xhtml) for details on the various strip types.

### Track Menu

Contains tools for working with NLA tracks.
See [Editing Tracks](editing/track.xhtml) for details.

### Strip Menu

Contains tools for working with NLA strips.
See [Editing Strips](editing/strip.xhtml) for details.

### Filters

Only Show Selected
:   Only shows tracks belonging to objects that are selected.

Show Hidden
:   Shows tracks from objects that are hidden.

Include Missing NLA
:   Shows the Action Track even if there is no action in it.

Search
:   Filters the track list by a search term.

Filtering Collection
:   Select a collection to only show tracks from objects in that collection.

Filter by Type
:   Filter tracks by target type.

Sort Data-Blocks
:   Sorts data-blocks alphabetically to make them easier to find.

    If your playback speed suffers because of this
    (should only really be an issue when working with lots of objects),
    you can turn it off.

### Snap

The toggle button enables/disables automatic strip snapping.
The dropdown button shows a popover with the following options:

Snap To
:   Type of element to snap to.

    Frame:
    :   Snap to full frames.

    Second:
    :   Snap to seconds.

    Nearest Marker:
    :   Snap to the nearest [Marker](../../animation/markers.xhtml).

Absolute Time Snap
:   When disabled, strips will move in increments of *Snap To*.
    For example, if you selected *Second* and have a strip that currently
    starts on 0:06+5, dragging it to the right will snap it to 0:07+5. Its time
    increases by a second, and its subsecond offset of 5 frames remains the same.

    When enabled, strips will snap to multiples of *Snap To*.
    Taking the above example, the strip would snap to 0:07+0,
    removing the subsecond offset.