Changing the actions of the mouse buttons PuTTY's copy and paste mechanism is modelled on the Unix xterm application. The X Window System uses a three-button mouse, and the convention is that the left button selects, the right button extends an existing selection, and the middle button pastes. When running one of these applications, pressing the mouse buttons no longer performs copy and paste. If you do need to copy and paste, you can still do so if you hold down Shift while you do your mouse clicks. This panel allows you to control precisely what is considered to be a word.
PuTTY considers a single word to be any number of adjacent characters in the same class.
Class 1 contains most punctuation. In order to adjust these assignments, you start by selecting a group of characters in the list box.