title: Where are bitbake python functions documented
body: <p>I'm trying to find documentation for "bb.utils.contains".
  I found the code in pokey/bitbake/lib/utils.py, but that code is poorly documented.
  For instance, it takes a parameter named "d".  What is "d"?
  How do you even get started with a short non-descriptive name like that?</p>
  
  <p>I've downloaded and searched all the yocto and poky documents, and performed a number
  of web searches, to no avail.</p>
  
  <p>Does anybody know of a good reference to the built in bitbake python utilities?</p>