We report on the initial stages of development of a robust parsing system, to be used as part of The Editor's Assistant, a program that detects and corrects textual errors and infelicities in the area of syntax and style. Our mechanism extends the standard PATR-n formalism by indexing the constraints on rules and abstracting away control of the application of these constraints. This allows independent specification of grouping and ordering of the constraints, which can improve the efficiency of processing, and in conjunction with information specifying whether constraints are necessary or optional, allows detection of syntactic errors.