Embedded pushdown automaton

An embedded pushdown automaton (EPDA) is a computational model for parsing languages generated by tree-adjoining grammars (TAGs). It is similar to the context-free grammar-parsing pushdown automaton, but instead of using a plain stack to store symbols, it has a stack of iterated stacks that store symbols, giving TAGs a generative capacity between context-free and context-sensitive grammars, or a subset of mildly context-sensitive grammars.

Source: Wikipedia — Embedded pushdown automaton (CC BY-SA 4.0)