What represents 'StartupWMClass' entry from a .desktop file in Ubuntu?

Question

I am very new in developing application under Linux.

I have a doubt regarding about the use of .desktop file to add an icon into the Ubuntu Unity toolbar.

I have the following .desktop file:

[Desktop Entry]
Type=Application
#Exec=/usr/share/ConnectDataSpace/appl/launcher.sh
Exec=/usr/share/XCloud/appl/launcher.sh
Type=Application
X-GNOME-Autostart-enabled=true
#Name[en_US]=Connect Data Space
Name[en_US]=XCloud
#Name=Connect Data Space
Name=XCloud
Comment[en_US]=
Comment=
StartupNotify=true
OnlyShowIn=GNOME;Unity;
#StartupWMClass=ConnectDataSpace
StartupWMClass=XCloud
#Icon=/usr/share/ConnectDataSpace/img/icoLauncher.png
Icon=/usr/share/XCloud/img/icoLauncher.png

My doubt is: What exactly represents the StartupWMClass=XCloud field of this file?

Answer 1

StartupWMClass - If specified, it is known that the application will map at least one window with the given string as its WM class or WM name hint (see the Startup Notification Protocol Specification for more details).

Source: Recognized desktop entry keys