Strains of programming are essentially how the author interprets how programming exists literally, within the context of the construct.  In this vision the strains are much the same as DNA in humans.  This is only an abstraction, based upon experience and observations, not literal.  Maintaining this perspective on programming allows for easy, fluid modifications, augmentations, alterations, and understanding of constructs.  The strain is simultaneously in every place within the construct, again, similar to how DNA is in every cell of the body. 

The real beauty of this model of interpretation is that you can simply tack on tracts of strain to the construct’s strain that allow whatever you want (much like genetic engineering).  In layman’s terms: you can take things you want from other constructs and put them in other ones.

(Aren’t you glad you actually look at all the pages now? Back button twice)