What is the burden of proving a prior conviction for sexual assault?

conviction does not reveal how the offense was committed and the offense can be committed in multiple ways, a factfinder must presume the conviction was for the least serious form of the offense. On review, we examine the record in the light most favorable to the judgment to determine whether a rational factfinder could have found the prosecution sustained its burden of proving the prior conviction allegations beyond a reasonable doubt. (People v. Miles (2008) 43 Cal.4th 1074, 1082-1083.)