1. A method of placing printing assist features in a mask layout, the method comprising: providing a design layout having one or more designed features; generating a set of parameters, said set of parameters being associated with one or more printing assist features (PrAFs); adding said one or more PrAFs of said set of parameters to said design layout to produce a modified design layout; performing simulation of said one or more PrAFs and said one or more designed features on said modified design layout; verifying whether said one or more PrAFs are removable based on results of said simulation; and creating a set of PrAF placement rules based on said set of parameters, if said one or more PrAFs are verified as removable.