Visualization commands for handling views

• GEANT4 user commands are installed by writing classes G4XXXMessenger: public G4UImessenger
• Installed commands are stored in a tree structure beginning from `/' (root)
• Basic visualization commands are already supported by the class G4VisManMessenger.
• C++ programmers can easily add his own command by editing or creating a G4XXXMessenger.
• GUI's based on Java, Tcl/Tk, Wo, and XVT are available
  • In the following, we explain existing visualization commands in ``command-line mode'' for convenience in documentation.

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 FIG      : GEANT4 GUI (Java version)
 File Name: G4GUI_JAVA.ps
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 FIG      : GEANT4 GUI (Tcl/Tk version)
 File Name: G4GUI_TCL_TK.ps
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 FIG      : GEANT4 GUI (XVT version)
 File Name: G4GUI_XVT.ps
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