Past convictions

I recently learnt that Jurors and Judges are not informed of prior convictions during a trial, I found this rather astonsishing.

Should or should prior convictions be mentioned during a hearing?

The purple frog is circumstantial evidence at best -- it in no way places the defendant at the scene of the crime in lieu of a framejob or a copycat criminal.  Guilt must be determined beyond a reasonable doubt, so unless there is significant corroborating evidence to support the frog theory, it shouldn't be admissible.