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El Salvador
Practice Relating to Rule 101. The Principle of Legality
El Salvador’s Penal Code (1997), as amended to 2008, which contains a section on violations of the laws or customs of war, states in its general provisions:
No one may be punished for an act or omission that was not defined by criminal law, in a precise and clear manner, as an offence or a fault, nor can a person be punished or made the object of a security measure if the law was not in force prior [to when the offence was committed]. 
El Salvador, Penal Code, 1997, as amended to 2008, Article 1.
In its concluding general section, the Penal Code further states: “All persons accused of offences or faults, at the time this Code enters into force, will benefit from the application of the more favourable provisions contained either in this law or in the derogated one.” 
El Salvador, Penal Code, 1997, as amended in 2008, Article 407.