Unconditional Surrender - Surrender at Discretion

In siege warfare, the demand that the garrison unconditionally surrender to the besiegers is traditionally phrased as "surrender at discretion." For example, at the siege of Stirling during the 1745 Jacobite Rebellion:

Charles, thereupon, sent a verbal message to the magistrates, requiring them instantly to surrender the town; but, at their solicitation, they obtained till ten o'clock next day to make up their minds. The message was taken into consideration at a public meeting of the inhabitants, and anxiously debated. The majority having come to the resolution that it was impossible to defend the town with the handful of men within, two deputies were sent to Bannockburn, the head-quarters of the Highland army, who offered to surrender to terms; stating that, rather than surrender at discretion, as required, they would defend the town to the last extremity. After a negotiation, which occupied the greater part of Tuesday, the following terms of capitulation were agreed upon: . .

It was also seen at the Battle of the Alamo, when Santa Anna asked Jim Bowie and William B. Travis for unconditional surrender. Even though Bowie wished to surrender unconditionally, Travis refused, retaliated by firing a cannon at Santa Anna's army, and wrote in his final dispatches:

The enemy has demanded a surrender at discretion otherwise the garrison are to be put to the sword, if the fort is taken — I have answered their demand with a cannon shot, and our flag still waves proudly from the walls — I shall never surrender or retreat.

The phrase surrender at discretion is still used in treaties, for example the Rome Statute that entered into force on July 1, 2002, specifies under "Article 8 war crimes, Paragraph 2.b" that:

Other serious violations of the laws and customs applicable in international armed conflict, within the established framework of international law, namely, any of the following acts:

...

(vi) Killing or wounding a combatant who, having laid down his arms or having no longer means of defence, has surrendered at discretion;

This wording in the Rome Statute is taken almost word for word from Article 23 of the 1907 IV Hague Convention The Laws and Customs of War on Land: "...it is especially forbidden - ... To kill or wound an enemy who, having laid down his arms, or having no longer means of defence, has surrendered at discretion", and is part of the customary laws of war.