Universal interface of TAUOLA : technical and physics documentation

Because of their narrow width, τ decays can be well separated from their production process. Only spin degrees of freedom connect these two parts of the physics process of interest for high energy collision experiments. In the following, we present a Monte Carlo algorithm which is based on that property. The interface supplements events generated by other programs, with τ decays. Effects of spin, including transverse degrees of freedom, genuine weak corrections or of new physics may be taken into account at the time when a τ decay is generated and written into an event record. The physics content of the C++ interface is already now richer than its FORTRAN predecessor.