Interestingly, some recent works<cite> [13,</cite> 18] indicate that string kernels can yield robust results in the cross-domain setting without any domain adaptation. In fact, methods based on string kernels have demonstrated impressive results in various text classification tasks ranging from native language identification [22] [23] [24] 36] and authorship identification [34] to dialect identification [4, 18, 21] , sentiment analysis<cite> [13,</cite> 35] and automatic essay scoring [7] .