From the code of federal record CFR Title 32 Subtitle A Chapter V Subchapter F Part 575 Section 575.2
https://www.law.cornell.edu/cfr/text/32/575.3
(a) Congressional / Gubernatorial Nomination.
(1) Up to 10 nominations may be submitted for each vacancy. Nominating authorities may use one of three methods of nomination:
(i) Name 10 nominees on a totally competitive basis,
(ii) Name a principal nominee, with nine competing alternates, or
(iii) Name a principal nominee, with nine alternates in order of preference.
(2) The priority that a fully qualified candidate may receive when considered for appointment is actually governed by the method of nomination used. For example, a principal nominee who is found minimally qualified must be offered an appointment. Conversely, the same individual nominated on a totally competitive basis, may be ranked as one of the least qualified nominees for that vacancy and, consequently, may not be offered an appointment. Many nominating authorities hold preliminary competitive nomination examinations to select their nominees. Those selected are required to be actual residents of the geographic location represented by the nominating authority.