The
click right on the viewer window gives access to the contextual menu.
There are various submenu on it, including the "SELECTION" submenu,
which opens possible selection methods (such as select all atoms, invert selection). In this submenu there is also a shortcut to the Advanced Selection Tool. Many
entries of the contextual menu are self-explanatory. "Toggle" actions
means that if one corresponding object is already present (such as
label, thermal ellipsoids, axis system..), then all are deleted, but if
none is present, they are all showed. "SYMMETRY
OPERATIONS" submenu gives actions related to symmetry operations and
crystal packing : generate symmetry mates to fill unit cell, show
possible symmetry equivalent molecules center-of-mass positions etc... "CONSTRAINTS"
submenu permits to show all electron density constraint of one type
(valence, multipolar, kappa) at one time, and to remove them all. They
are an alternate ways to show constrains than using the main toolbar buttons. "MEASUREMENTS" submenu allows to hide the last measurement (distance, angle ....) or to remove all of them."WATER MOLECULES" and "HYDROGEN ATOMS" submenus allow of course to show/hide water molecules or hydrogen atoms, respectively.

When
atoms or critical points are selected, the "SELECTED ATOMS" and/or
"SELECTED CPs" submenu become available, and give access to actions
that will be performed on selected objects only.

Again
the various entries are rather clear, only the "CONSTRAINTS" entry
needs some explanations. It opens another submenu allowing to toggle
various constrains, but also to create electron density constrains
using the "constrain charge density" option. choosing this option opens
the "Constrain maker" dialog window, which will allow the user to
constrain together all currently selected atoms
electron density valence, multipolar and/or kappa/kappa prime
parameters. The created constrains will be written in the selected
CONSTRAIN MoPro file.

The
selection itself corresponds to a list of selected atoms. They are
visible on screen as they are surrounded with a colored shape, on the
below image for instance, 8 atoms are selected and surrounded by purple
wires.

The
number of currently selected atoms is always written in the top right
corner of the Viewer. Atoms can be selected and added to the selection
using left mouse button click on atoms, using the selection rectangle
(see program overview), using shortcuts such as "Select All"
from contextual menu, using the "Advanced Selection Tool" or using the "Object tree". On the example below the atoms NT, H1 and H3 have been selected from the tree.

The
selection can be saved at any time using the "SELECTION" submenu then
"Save current selection" option. The saved selection can afterward be
recalled (erasing the current one) or added to the current
selection.