When there is an imperfect description, or when no person or property exactly answers the description, mistakes and omissions must be corrected, if the error appears from the context of the will or from extrinsic evidence, excluding the oral declarations of the testator as to his intention; and when an uncertainty arises upon the face of the will, as to the application of any of its provisions, the testator's intention is to be ascertained from the words of the will, taking into consideration the circumstances under which it was made, excluding such oral declarations. (n)