Guide

Range Slide Selection

With the Shift key pressed, selecting a slide that is not the current one will select all slides in the range between the current slide and the slide clicked with Shift.

In the Editing Window, when no element is selected, using Shift+Left/Right with the keyboard also selects a range similarly.

Aside from Range Slide Selection, there is an easy way to select all. In the Editing Window, when no element is selected, press Ctrl+A to select all slides.