The formalism was introduced in the slightly more constrained form of Discontinuous-constituent Phrase Structure Grammar with Subscripts and Deletes (DCPSGsd) in Harman (1963).
[1] DCPSGs describe a superset of the context-free languages, by means of rewrite rules that permit a limited amount of wrapping, similar to that found in Head grammar.
Rewrite rules of a DCPSG are identical to those of a CFG, with the addition of a meta-symbol, denoted here as an underscore.
DCPSG rules therefore have the general form
being inserted immediately after the next non-terminal that is introduced at the same time.
is simply inserted immediately after the non-terminal that follows
We can characterize the gross sentence structure of a VSO language such as Irish with the following rules (substituting English words for Irish words, and using subscripts solely for demonstration of discontinuity): A derivation for the sentence saw John Susan, where John is the subject, and Susan is the direct object forming a VP with saw is: