This paper is concerned with the detection and correction of sub-sentential English text errors. Previous spelling programs, unless restricted to a very small set of words, have operated as post-processors. And to date, grammar checkers and other programs which deal with ill-formed input usually step directly from spelling considerations to a full-scale parse, assuming a complete sentence. Work described below is aimed at evaluating the effectiveness of shallow (sub-sentential) processing and the feasibility of cooperative error checking, through building and testing appropriately an error-processing system. A system under construction is outlined which incorporates morphological checks (using new two-level error rules) over a directed letter graph, tag positional trigrams and partial parsing. Intended testing is discussed.