This paper argues that the dominant framework for conceptualizing validation evidence and analysis--the "five sources" framework from the 1999 "Standards"--is seriously limited. Its limitation raises a significant barrier to understanding the nature of comprehensive validation, and this presents a significant threat to effective validation practice. Motivated by a belief that "validity by design" ought to be substantiated through "validation of design" this paper demonstrates the importance of adopting a broader conceptual framework. It introduces a new framework, based upon the metaphor of different validation lenses through which to scrutinize assessment procedures at differing levels of detail, with micro-validation lenses at one end of a continuum and macro-validation lenses at the other. The evolution of validation theory can be seen as a very gradual, if somewhat reluctant, acknowledgement of the importance of micro-validation. This paper recommends micro-validation as the natural foundation for any comprehensive validation program.