Related Rule
Belgium
Practice Relating to Rule 106. Conditions for Prisoner-of-War Status
Belgium’s Law of War Manual (1983) states that there is a “customary rule according to which all members of the regular armed forces wear a uniform”. 
Belgium, Droit Pénal et Disciplinaire Militaire et Droit de la Guerre, Deuxième Partie, Droit de la Guerre, Ecole Royale Militaire, par J. Maes, Chargé de cours, Avocat-général près la Cour Militaire, D/1983/1187/029, 1983, p. 20.
Belgium’s Law of War Manual (1983) states:
The population of a non-occupied territory who spontaneously take up arms to resist the invading forces without having had time to form themselves into an organized resistance movement or to join the regular armed forces are considered combatants on the condition that this population:
a. respects the laws and customs of war;
b. carries arms openly. 
Belgium, Droit Pénal et Disciplinaire Militaire et Droit de la Guerre, Deuxième Partie, Droit de la Guerre, Ecole Royale Militaire, par J. Maes, Chargé de cours, Avocat-général près la Cour Militaire, D/1983/1187/029, 1983, p. 20.
In 1991, a Belgian parliamentary report considered that in the case of a levée en masse, actions in defence of the territory are permitted and justified by law even if they are not ordered by a proper authority. 
Belgium, Senate, Report, Enquête parlementaire sur l’existence en Belgique d’un réseau de renseignements clandestin international, 1990–1991 Session, Doc. 1117-4, 1 October 1991, § 24.
Belgium’s Law of War Manual (1983) states:
Recognizing, however, that there are situations in armed conflicts where, owing to the nature of the hostilities an armed combatant cannot so distinguish himself, he shall retain his status as a combatant, provided that, in such situations, he carries his arms openly:
(a) during each military engagement, and
(b) during such time as he is visible to the adversary while he is engaged in a military deployment preceding the launching of an attack in which he is to participate.
Acts which comply with the requirements of this paragraph shall not be considered as perfidious. 
Belgium, Droit Pénal et Disciplinaire Militaire et Droit de la Guerre, Deuxième Partie, Droit de la Guerre, Ecole Royale Militaire, par J. Maes, Chargé de cours, Avocat-général près la Cour Militaire, D/1983/1187/029, 1983, pp. 20–21.
It would be preferable that Belgium only supports this rule on condition that it does not apply to operations on non-occupied Belgian territory. The term “military deployment” should, on the other hand, be interpreted very widely in the sense that it covers every movement towards the place from which an attack is to be launched. To be “visible” includes being able to “be observed” even at night by means of infrared rays and the notion “adversary” should be clarified. 
Belgium, Droit Pénal et Disciplinaire Militaire et Droit de la Guerre, Deuxième Partie, Droit de la Guerre, Ecole Royale Militaire, par J. Maes, Chargé de cours, Avocat-général près la Cour Militaire, D/1983/1187/029, 1983, p. 21.
Upon ratification of the 1977 Additional Protocol I, Belgium stated:
With respect to Article 44, the Belgian Government declares that the armed conflict situations described in paragraph 3 can arise only in occupied territory or in the armed conflicts covered by Article 1, paragraph 4, of the Protocol. Furthermore the Belgian Government interprets the term “deployment” used in subparagraph (b) of the said paragraph 3 as comprising any individual or collective movement towards a position from which an attack is to be launched. 
Belgium, Interpretative declarations made upon ratification of the 1977 Additional Protocol I, 20 May 1986, § 4.