For the SqlPanel, the Explorer.props file must contain the following
lines:

Tabs=wekaexamples.gui.explorer.SqlPanel,\
      weka.gui.explorer.ClassifierPanel,\
      weka.gui.explorer.ClustererPanel,\
      weka.gui.explorer.AssociationsPanel,\
      weka.gui.explorer.AttributeSelectionPanel,\
      weka.gui.explorer.VisualizePanel
      
For the GeneratorPanel, the following lines:

Tabs=wekaexamples.gui.explorer.GeneratorPanel:standalone,\
     weka.gui.explorer.ClassifierPanel,\
     weka.gui.explorer.ClustererPanel,\
     weka.gui.explorer.AssociationsPanel,\
     weka.gui.explorer.AttributeSelectionPanel,\
     weka.gui.explorer.VisualizePanel

And for the ExperimentPanel, the following lines:

Tabs=weka.gui.explorer.ClassifierPanel,\
     wekaexamples.gui.explorer.ExperimentPanel,\
     weka.gui.explorer.ClustererPanel,\
     weka.gui.explorer.AssociationsPanel,\
     weka.gui.explorer.AttributeSelectionPanel,\
     weka.gui.explorer.VisualizePanel

See also wiki article "Adding tabs in the Explorer":
  http://weka.wiki.sourceforge.net/Adding+tabs+in+the+Explorer
