Règle correspondante
Sweden
Practice Relating to Rule 65. Perfidy
Section A. General
Sweden’s IHL Manual (1991) considers that the prohibition of perfidy as contained in Article 37 of the 1977 Additional Protocol I is part of customary international law. 
Sweden, International Humanitarian Law in Armed Conflict, with reference to the Swedish Total Defence System, Swedish Ministry of Defence, January 1991, Section 2.2.3, p. 18.
The manual states:
Sweden and several other countries wished the [prohibition of perfidy] to be inserted in Additional Protocol II as well, since perfidy is probably equally common in internal conflicts. The majority were against this, however, the main reason being that, in conflicts of this type, particular difficulties may arise in determining exactly what may be considered perfidy.
The concept of perfidy, or perfidious conduct which is a more adequate expression, is defined as acts inviting the confidence of an adversary giving the acting party a legally protected status. This protection is abused in order to kill, injure or capture the adversary’s soldiers. Perfidy thus means that one party deliberately and on false grounds invites the confidence of the other in order then to betray this confidence by acts of violence. It should be added that perfidy, as defined in Article 37 [of the 1977 Additional Protocol I], refers to acts against persons, but does not include sabotage or the destruction of property …
Only where protected status is employed for killing, injuring or capturing the adversary is the act considered as perfidy …
Accusations of perfidy are always judged to be extremely grave, since a crime against Article 37 [of the 1977 Additional Protocol I] shall according to the bases of Additional Protocol I be viewed as a grave breach of international humanitarian law. 
Sweden, International Humanitarian Law in Armed Conflict, with reference to the Swedish Total Defence System, Swedish Ministry of Defence, January 1991, Section 3.2.1.1.b, pp. 28–30.