What kind of a presumption lies in favour of a power of attorney?

S. 85. Presumption as to powers-of-attorney. –– The Court shall presume that every document purporting to be a power-of-attorney, and to have been executed before, and authenticated by, a Notary Public, or any Court, Judge, Magistrate, Indian Consul or Vice-Consul, or representative of the Central Government, was so executed and authenticated. Shall presume marks a rebuttable presumption in favour of power of attorney which can be rebutted if evidence is given against it.