Microsoft developed the channel definition format (CDF) as an application of the eXtensible markup language (XML), proposing it as a standard for push media. CDF allows Web publishers to push content at users through a channel, similar to Marimba's Castanet or Netscape's NetCaster. New content posted to a channel's Web server will push any software that supports the CDF format. One piece of software that doesn't support CDF, however, is anything written by Netscape, which uses its own NetCaster. While Microsoft has an advantage in working with the World Wide Web Consortium (W3C), it hasn't yet defined a user interface for the channels. Conversely, Marimba and Netscape aren't overtly trying to write a standard specification.