bitmap caching question

[stephenfinn]

could someone clear up this for me?
does bitmap caching only apply to vector images? that would seem to make sense; a vector is turned into a bitmap then moved much quicker around the screen because the vectors don't have to be worked out every frame. however, i saw this :
http://www.brokenbutton.com/fp8testpng.html
which suggests that it works for bitmaps too. can anyone explain this?

[hangalot]

bitmaps are drawn to vectors in order to render by the flash player hence that result being acheived

[stephenfinn]

so the png is converted to vectors via the cacheAsBitmap?

[hangalot]

everything in flash is converted to vectors, cacheAsBitmap just means that section does not get redrawn. but if it is invalidated you start getting nasty performance issues