Slicer  5.3
Slicer is a multi-platform, free and open source software package for visualization and medical image computing

Widgets → Base Relation

File in Modules/Loadable/VolumeRendering/WidgetsIncludes file in Base
qSlicerVolumeRenderingModuleWidget.hQTGUI / qSlicerAbstractModuleWidget.h
qSlicerVolumeRenderingPresetComboBox.hQTGUI / qSlicerWidget.h