Unfortunately the rules for method specificity are not given in the Julia manual. I think the details are rather complicated, so the developers do not want to codify a list of specificity rules by putting them in the manual. There’s a brief discussion of method specificity in the developer docs:
https://docs.julialang.org/en/v1/devdocs/types/#Subtyping-and-method-sorting
Also take a look at this video:
