Lex Sessions Lex contains two main windows, each of which in turn contains tab windows. The tab windows in the upper main window are used to access dictionary and grammar sites. The tab windows in the lower main window are used to access the sites that you choose to work on. A setup of tab windows accessing various web sites is called a Lex session. If you are viewing this web page in Lex you can start and save sessions directly from the tables below.