1. A computer-implemented method of searching a structured document for text having relevance to a given set of terms, using a processor, the method comprising: receiving a node set corresponding to at least one fragment of the structured document, wherein the fragment includes at least a portion of text of the structured document and at least one corresponding pre-computed step query; receiving at least one search term; receiving a pre-computed lookup index with entries corresponding to the fragments, each entry having an associated subtree identifier; searching the lookup index with the search terms; returning a set of resulting step queries indicated by the lookup index and corresponding to the search terms; assessing an intersection of the resulting step queries with the given set of terms, wherein the resulting step queries each have an associated subtree identifier; and retrieving a node set associated with the intersection and corresponding to a fragment.
3. The method of claim 1 , further comprising retrieving a subtree fragment corresponding to a subtree identifier.