30. The non-transitory computer readable medium of claim 29 , wherein instructions for selectively associating the propagating attribute with each parse item of the plurality of parse items located in the direction of propagation within the ordered data structure include instructions for associating the propagating attribute with each parse item of the plurality of parse items located in the direction of propagation within the ordered data structure until association of the propagating attribute is blocked.
29. A non-transitory computer readable storage medium encoded with instructions executable by a processor, the instructions comprising: identifying 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; determining a direction of propagation of the propagating attribute within the ordered data structure; and selectively associating the propagating attribute with each parse item of the plurality of parse items located in the direction of propagation within the ordered data structure.