<group>is the group name of commands and
<function>is the function name of the command. An extension may have a set of commands, so typically the group name is the extension name. For example, the ID of the command showing a message of HelloWorld extension is
app.commands.registermethod. The first parameter is the ID of the command and the second is the handler function and the third (optional) is the display name of the command (Shown in Command Palette).
helloworld:show-messagecommand. It can be called manually as follow: