16. The apparatus of claim 15 , wherein the prefix comprises N leading characters of the marked word, and N is 3 or less.
15. An apparatus for indexing a corpus of documents, wherein the words in the corpus of documents include a set of words having a characteristic to be subject of queries, comprising: a data processor arranged to parse documents in the corpus of documents to identify words found in the documents and locations of the words in the documents, and to create an index structure including entries representing words found in the corpus of documents mapping entries in the index structure to locations of the words in documents in the corpus memory storing the index structure writable and readable by the data processor; wherein the data processor includes an indexing processor which indentifies words in a set of words having a characteristic represent d by a mark in a set of marks, and add entries in the index structure representing marks for the identified the set mapping the marks to the locations of the identified words, and wherein one or more entries representing marks include fewer, if any, than all of the characters of the corresponding identified words; wherein entries in the index structure representing the marks comprise tokens coalesced with prefixes of respective marked words, the prefixes comprising one or more leading characters of the respective marked words.