A media monitoring service, a press clipping service or a clipping service as known in earlier times, provides clients with copies of media content, which is of specific interest to them and subject to changing demand; what they provide may include documentation, content, analysis, or editorial opinion, specifically or widely. These services tend to specialize their coverage by subject, industry, size, geography, publication, journalist, or editor. The printed sources, which could be readily monitored, greatly expanded with the advent of telegraphy and submarine cables in the mid- to late-19th century; the various types of media now available proliferated in the 20th century, with the development of radio, television, the photocopier and the World Wide Web. Though media monitoring is generally used for capturing content or editorial opinion, it also may be used to capture advertising content.