VLF-ONE has more extensive message handling features than VLF-ONE.
To understand these capabilities use the shipped Example Application -> Basic -> Messages,
The source code is in DF_MSGEXO.
The key concepts are
That the main web browser form and individual filter and handler 'panes' have their own message area
That messages can be classified as informational, warning or fatal which influences how they display.
That message may have second level text.