The current text of MPEP 2111.05, if read quickly, seems to suggest that a "function" of "descriptive material" itself carries patentable weight. But this interpretation is not correct: A sheet of instructions as part of the kit claim in In re Ngai (cited in this section) was found to *not* have patentable weight. The "functional" nature of the particular instructions did not save the claims from anticipation over a prior art kit, even though the method in that same application was allowable. It cannot be the case that the "function" itself in descriptive material dictates patentable weight; had that been true, Ngai would have ended in a reversal for the examiner.
The dispositive factor of In re Gulack and In re Ngai was the relationship to the substrate. Ngai states "This case, however, is dissimilar from Gulack. There the printed matter and the circularity of the band were *interrelated*, so as to produce a new product useful for “educational and recreational mathematical” purposes. Here, addition of a new set of instructions into a known kit does not *interrelate* with the kit in the same way as the numbers interrelated with the band." (emphasis added) Although both cases involved a function associated with the descriptive material, it was the interrelation that was key to whether there was patentable weight.
This meaning of MPEP 2111.05 might be clearer to readers if the subsection titles emphasized that the "functional relationship" is between the "descriptive material" and the "substrate." The substantive text could be mostly left as is, since the subsection headings would provide much needed context.