Practice relating to Rule 66. Non-Hostile Contacts between the Parties to the Conflict
New Zealand’s Military Manual (1992) provides:
Even between the belligerent armies direct contact may sometimes be necessary [for instance to arrange for the collection of the dead or exchange of the wounded] but relations between the belligerent forces are confined to mainly military matters. Occasionally, such relations, for example, the arrangement of a local truce or surrender, may involve political considerations but in view of radio and similar means of communication these matters tend nowadays to be taken up on an inter-government level, avoiding actual negotiations between belligerent commanders.
Negotiations between belligerent commanders are normally conducted, at least in the first instance, by intermediaries known as parlementaires. The wish to negotiate by parlementaires is frequently indicated by the raising of a white flag but any other method of communication, eg by radio, may be employed.
Any agreement made by belligerent commanders must be scrupulously adhered to … As between combatants, the most usual purpose of contact is to arrange for an armistice or truce, whether for a specific purpose or more generally. Whatever the nature of the arrangement it must be entered into and carried out in good faith.
Agreements between belligerents permitting activities between them which are inconsistent with belligerent status are known as cartels. Such an arrangement is voidable by either Party on proof of breach of its terms by the other.
… In addition to any other agreements that may be made between the belligerents or commanders in the field, the Geneva Conventions and [Additional Protocol] I contain a number of provisions recognizing that in the special circumstances specified in these treaties agreements between belligerents may be desirable or necessary.