20. A computer system comprising a processor coupled to a memory, wherein the memory is encoded with computer executable instructions that when executed cause the processor to: identify a propagating attribute associated with a parse item of a plurality of parse items, the plurality of parse items arranged in an ordered data structure; determine a direction of propagation of the propagating attribute within the ordered data structure; and selectively associate the propagating attribute with each parse item of the plurality of parse items located in the direction of propagation within the ordered data structure.
20. A computer system comprising a processor coupled to a memory, wherein the memory is encoded with computer executable instructions that when executed cause the processor to: identify a propagating attribute associated with a parse item of a plurality of parse items, the plurality of parse items arranged in an ordered data structure; determine a direction of propagation of the propagating attribute within the ordered data structure; and selectively associate the propagating attribute with each parse item of the plurality of parse items located in the direction of propagation within the ordered data structure. 28. The computer system of claim 20 , wherein the instructions further cause the processor to arrange the plurality of parse items in a linked list.