1. An apparatus for contextual match in a corpus of documents, comprising: a data processor arranged to execute queries to match words in the corpus of documents; memory storing an index structure readable by the data processor, the index structure mapping entries in the index structure to locations of words in the documents in the corpus, the index structure including entries representing words found in the corpus of documents, and entries representing marks which identify a characteristic of corresponding marked words, and wherein one or more entries representing marks include fewer, if any, than all of the characters of the corresponding marked words; wherein the data processor includes a query processor which modifies a subject query to form a modified query adapted to use the entries representing marks, and executes the modified query using said index structure; wherein at least one entry representing a mark in the index structure comprises a token representing a type of mark coalesced with a prefix of a corresponding marked word, the prefix comprising one or more leading characters of the corresponding marked word.