* [index-reverse](index-reverse/) is code for `word->document` indexes. There are two such indexes, one containing only document-word pairs that are flagged as important, e.g. the word appears in the title or has a high TF-IDF. This allows good results to be discovered quickly without having to sift through ten thousand bad ones first.
* [index-forward](index-forward/) is the `document->word` index containing metadata about each word, such as its position. It is used after identifying candidate search results via the reverse index to fetch metadata and rank the results.
