Yosef Karo

“ One who is coming to affix [a mezuzah] should place it in a reed or other type of tube and he should affix it in its place and say the placing “who sanctified us with His commandments and commanded us to affix a mezuzah” and one should not make a blessing when the mezuzah is being written. Rema: One who is affixing two or three mezuzot should make one blessing for all of them. ”

“ In the empty space of the doorway [on the inside of the doorway] within the tefach that is closest to the outside, Rema: And if he changes [and places it somewhere else] it does not prevent [the fulfillment of the mitzvah] so long as he places it on the doorpost itself. [Place it] at the start of the upper third of the height of the entryway; and if he attached it higher than this it is valid, so long as it is at least a tefach way from the lintel, and one should attach it on the right side [of the doorway from the point of view] of entering. ”