The definition of optimal correspondent subsequence (OCS), which extends the finite alphabet editing error minimization matching to infinite alphabet penalty minimization matching, is given. The authors prove that the string distance derived from OCS is a metric. An algorithm to compute the string-to-string OCS is given. The computational complexity of OCS is analyzed. OCS is more efficient than relaxation and elastic matching for 1D problems. An algorithm combining syntactic information in template matching is given to show the ease of integrating regular grammar into the OCS technique. Since in different applications different penalty functions may be required, two of them are discussed: one pointwise and the other piecewise. The pointwise application consists of a stereo epipolar line matching problem solved by using string-to-string OCS. The feasibility of applying OCS to UPC bar-code recognition is investigated, showing the elegance of string-to-regular-expression OCS compared to the relaxation and elastic matching techniques.>