The common way to build stellar models is to treat the radiation zones as inert, stable regions, in contrast with the well mixed convection zones. This allows to account for the main features of stellar evolution, such as the main sequence and the existence of red giants. But there are many indications that some mixing occurs within the radiation zones, and that it has an impact on the later stages. 
Manuel Forestini was one the first to undertake the implementation of such mixing in his stellar code, and thus to go beyond the standard model. Here I will briefly describe the mixing processes that are likely to operate in stellar radiation zones, as we understand them today, and discuss how well they account for the observed properties of stars.