itk_componet(hull) itk_interior

 itk_component add toolbar_frame {
       frame $itk_interior.tbf \
            -relief raised \
           -borderwidth 1
  }
 

same as:

 itk_component add toolbar_frame {
       frame $itk_component(hull).tbf \
            -relief raised \
           -borderwidth 1
  }

============

 itk_component add toolbar {
        frame $itk_interior.tbf.toolbar   
 }

same as

 itk_component add toolbar {
        frame $itk_component(hull).tbf.toolbar   
 }

same as

 itk_component add toolbar {
        frame $itk_component(toolbar_frame).toolbar   
 }