The name of the protocol handler may vary depending on the system.
The client parses the value of the attribute and checks whether such a protocol handler is already registered in the Windows Registry. If not, the handler is registered.
If you open an application link, the client which is defined for the specified URL is called and the call parameters are handed over to the server.
If several clients are used, e.g. development/test/productive system, each system should receive its own protocol name to open the appropriate system respectively.
The <command> describes a call with parameters which is linked to a particular action.
Customizing
To customize fields with application link, you can use buttons or link data fields.
You have to store a Python script for the data field.
If the user clicks on the button/link, the Python script is executed and sends a command to the client which contains the application link and possible call parameters.