lib: add clarification about the use of "prefix" in the docs.

[notmuch] / lib / database.cc

diff --git a/lib/database.cc b/lib/database.cc
index 9cf8062cbe7caa2c5f7ecd714ca934c7f96b1e76..f33f0af6a7145a603a7ed9eb42bed44c442deba4 100644 (file)
--- a/lib/database.cc
+++ b/lib/database.cc
@@ -63,14 +63,19 @@ typedef struct {
  * We currently have three different types of documents (mail, ghost,
  * and directory) and also some metadata.
  *
+ * There are two kinds of prefixes used in notmuch. There are the
+ * human friendly 'prefix names' like "thread:", which are also used
+ * in the query parser, and the actual prefix terms in the database
+ * (e.g. "G"). The correspondence is maintained in the file scope data
+ * structure 'prefix_table'.
+ *
  * Mail document
  * -------------
  * A mail document is associated with a particular email message. It
- * is stored in one or more files on disk (though only one has its
- * content indexed) and is uniquely identified  by its "id" field
- * (which is generally the message ID). It is indexed with the
- * following prefixed terms which the database uses to construct
- * threads, etc.:
+ * is stored in one or more files on disk and is uniquely identified
+ * by its "id" field (which is generally the message ID). It is
+ * indexed with the following prefixed terms which the database uses
+ * to construct threads, etc.:
  *
  *    Single terms of given prefix:
  *