The gutter is a strip on the left side of the text area that displays line numbers, and marker and position register locations. It is hidden by default. To show or hide the gutter, double-click on it (when it is collapsed, it is shown as a thin vertical line), or select Utilities>Gutter Expanded.
The gutter can be resized by dragging with the mouse. Resizing can sometimes be necessary if line numbers become too long to be displayed. To save the gutter's size for future sessions, right-click on it and select Save Gutter Size from the resulting context menu.
Many options relating to the gutter (colors, behavior, etc) can be changed in the Utilities>Global Options dialog box; see the section called The Global Options Dialog Box in Chapter 8 for details.
Figure 4-4. A view with the gutter showing