<runCommandButton> represents a button that attempts to execute the system command specified by a given text-valued property.
When the button is clicked, the value of the property is interpreted as a system command, and is executed.
If the value does not represent a valid system command for the current client platform, an error will occur. No attempt is made to validate the command before attempting to execute it.
If the value of the property is the empty string, the button should be disabled. If the client platform does not support execution of system commands, the button should be disabled.
The attributes for this element are described below: