include() like functionality for strings

Not sure what discussion has been done on this subject before, but here it goes. I wan't to be able to use a function that does the same thing as include, except instead of passing a file name I pass the actual string to be processed. This differs from eval() because the string may be all HTML. I've seen numerous hacks on how to get this functionality out of eval() such as prepending ?> and appending <? to your string, and creating temp files to include, etc. But this is somewhat ugly. I'm certain this function could be made easily, and if no one wants to do it simply point me in the direction where to find the code for include()/include_once() and I'm sure I can make something work. -Chris