[yocto] understanding what's in an image

[James Abernathy]

I'm trying to understand how bitbake parses the poky directory tree a little better.  

The best I can figure all .bb files are NOT included. Just some of them are.  I'm guessing that the .bb in the meta/recipe-sato named core-image-sato.bb is the one that is used to start the parsing if bitbake core-image-sato is executed.
I originally thought all subdirectories of a path included in BBLAYER were parsed looking for .bb files, but now I know that is not true, but not sure why.

For example, it does not appear that webkit is included in the core-image-sato even though the recipe-sato directory includes the webkit subdirectory with it's recipe.  What would be the proper way of adding the webkit to core-image-sato??

Jim A