1. A method of maintaining a search index, the method comprising: identifying one or more characteristics that are associated with particular data items that were excerpted from a first plurality of documents; selecting, from the one or more characteristics, one or more particular characteristics; and for each particular document in a second plurality of documents, performing steps comprising: determining whether to insert, into the search index, a candidate data item excerpted from the particular document, wherein determining whether to insert the candidate data item is based at least in part on whether the candidate data item is associated with characteristics in the one or more particular characteristics; and inserting the candidate data item into the search index in response to a determination that the candidate data item should be inserted.