1. A computer implemented method for designing a part, wherein the part is modeled by using: a seed structure of a context-free grammar, a set of rules of the grammar, at least two design features, each design feature being defined by at least one rule of the set, a priority order between the design features determined by the seed structure and the set of rules, the method comprising the steps of: displaying a representation of the part in a graphical user interface according to the priority order, modifying the priority order between said two design features by modifying the set of rules, and displaying a representation of the part according to the modified priority order.