Originally catalogs were just dealers' price lists, though today that is less common. The catalogs of some major publishers continue to serve as an official price list for the publisher. For example, Stanley Gibbons in the United Kingdom specifically states in the catalog that the price listed is the estimated selling price by Stanley Gibbons Ltd. On the other had, Scott in the United States does not sell stamps. Rather, the Scott catalog serves as a reference document for expected prices used by buyers and sellers. Over time, as philately developed, catalogs tended to accumulate additional supporting details about the stamps, such as dates of issue, color variations, and so forth. As their use by collectors became widespread, the catalogs came to define what was and was not a legitimate stamp, since many collectors would avoid stamps not described in the catalog. In recent years, the Internet has become a common resource for information about stamps. Some catalogs have an on-line version while others are available only on-line.