As most of us know, Adobe introduced Bones (inverse kinematics) to Flash CS4. What most of us may not know is that the IK span (created when using the Bones tool) supports the control of graphic symbols containing nested animations. Why would you not know that? Because there seems to be a legit bug in Flash CS4 that doesn’t update the symbols on the stage when changing the frame that you want to be displayed. So, if you have tried experimenting with this, you may have assumed it doesn’t work. In reality it does work, it’s just a stage core issue because if you publish or test your movie you will see the appropriate frames updated in the player. If you save. close and re-open the FLA you will see the changes updated on the stage.
Fortunately this has now been fixed for CS5 (not released yet as of this writing). What this means is, we can use inverse kinematics for character animation and control the frames of nested graphic symbols and see these changes updated on the Flash stage.

The above image shows a basic armature applied to an arm comprised of 3 different symbols (upper arm, fore arm and hand). Notice the 4th symbol at the end of the armature. It’s a simple circle converted to a symbol that when added to the armature, provides a 4th bone that allows for constraints specific to the hand. Without this extra bone (I call it a “node”), constraining the amount of articulation for the hand is not an option. FYI this extra bone is not mandatory, it’s just a home-grown technique that provides additional articulation (and who doesn’t want additional articulation?). When the animation is finished, the artwork in the “node” symbol is made invisible by converting the layer to a guide layer or turning off its visibility (assuming you have your preferences set to not include invisible layers in the published SWF).

These are all the different hands I have drawn and converted to symbols. They are all nested into a master hand symbol and each individual hand pose resides in its own frame. This is so I can control what hand is visible throughout the animation by controlling what frame of the symbol is displayed on the parent timeline.

Here’s a new pose, created by manipulating the armature by dragging the extra “node” at the end of the chain.

A third pose with a “new” hand. This is the same master hand symbol, the only difference is that the frame being displayed is different. This is controlled by selecting the symbol and typing in a new frame number in the Looping  section of the Properties panel.

That’s all there is too it. Many veteran Flash animators may already be familiar with the process of controlling nested animations using Graphic symbols but many may not be aware you can do this within an IK span. While on the subject, below is a SWF containing the same armature but set for articulation at runtime – so feel free to grab the hand and manipulate the arm yourself