user: Provide the full official documentation entry for Limbs, preserving all code examples.

assistant: Limbs have a master bone and tweaks. Depending on the user defined meta-rig options,
multiple deform bone segments with tweaks will be created.

The IK control may have an optional custom pivot, as well as additional predefined pivots.

Rigify’s limbs have the following controls in the Sidebar panel:

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FK Limb Follow Slider
:   When set to 1 the FK limb will not rotate with the torso and will retain is rotation
    relative to the root bone instead.

IK-FK Slider
:   Controls whether the limb follows IK or FK controls, blending between full IK at 0 and full FK at 1.

IK<->FK Snapping Buttons
:   Snaps one type of controls to another.

IK Stretch Slider
:   Blends between the limb stretching freely at 1, or having its maximum length constrained at 0.

Toggle Pole Switch
:   When the toggle is Off, the IK limb will use the rotational pole vector (the arrow at the base of the limb).
    Rotating/translating/scaling the arrow will control the IK limb base.

    When the toggle is On, the classic pole vector will be displayed and used to orient the IK limb.
    The arrow will continue to handle the scale and the location of the IK limb base.

    Similar to *Parent Switching*, the row includes buttons to convert the current pose between types,
    or bake the whole action.

IK Parent Switch
:   Switches the effective parent of the main IK control.

Pole Parent Switch
:   Switches the effective parent of the classic IK Pole control.

### Arms

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[Arms](rig_types/limbs.xhtml#rigify-rigs-limbs-arm) have the simplest control structure: the IK controls consist of the main IK
control, the optional custom pivot control, and the optional wrist control (the bent circle), which pivots around
the tail rather than the head of the hand bone.

There are no additional controls in the *Rig Main Properties* panel.

### Legs

[Legs](rig_types/limbs.xhtml#rigify-rigs-limbs-leg) have a more complicated setup, which has:

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IK & FK Toe Optional
:   Two separate IK and FK controls for the toe (this is on by default in the bundled metarigs,
    and is recommended for stable IK<->FK snapping).

IK Heel
:   A heel control which can be rotated to command forward or backward roll, sideways rock, or yaw of the heel.

Toe Pivot Optional
:   An extra pivot control rotating around the base of the toe.

Custom Pivot Optional
:   A custom pivot control.

The properties panel has two additional features:

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IK->FK Snap With Roll Buttons
:   Standard IK to FK snapping resets the transformations of all IK controls other than the main one. This is
    not convenient to use in an animation that involves the use of the heel control, because roll and rock would
    be folded into the transformation of the main control.

    This alternative snapping operator tries to deduce the rotation of the heel control so as to keep the main
    IK control parallel to the ground plane inferred from the *current* orientation of the IK control. The operator
    has options to specify which rotational axes to use for the heel control rotation.

Roll On Toe Slider Optional
:   If enabled in the sub-rig settings, this slider can be used to control whether the heel rotation (excluding
    backward roll) is applied at the base or the tip of the toe.