HTML is defined in practice both by Netscape and Microsoft as they add changes to their Web browsers and more officially for the industry by the World Wide Web Consortium (W3C). A new version of HTML called HTML 4 has recently been officially recommended by W3C, making this level an effective standard. However, both Netscape and Microsoft browsers currently implement some features differently and provide non-standard extensions. Web developers using the more advanced features of HTML 4 may have to design pages for both browsers and send out the appropriate version to a user. Significant features in HTML 4 are sometimes described in general as dynamic HTML.