From OpenSCADAWiki
For other operations you need to select an available child widget or a group of them, so let's see all features of the selection:
- SINGLE SELECTION — performed by single click the left mouse button above child widget, next click puts down the selection to widget under the previous one and up to this frame itself, unselecting child widgets. That is the widget stack transition at the fact.
- SELECTION BY WINDOW — performs the group selection of the child widgets by drawing a window around those widgets, starting the window from the left mouse button press on any unselected frame space and finishing on the button release.
- ADDITIVE SELECTION — you can append some child widgets to the selection holding the Shift key and performing whether single selection or by window. In the case of the single selection, the widget stack transition is turned off here, and instead triggering of the top widgets selection is actually turned on!