VMS Help TCPIP Services, TELNET, Debugging with TN3270  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Visible attribute mode provides a way to debug application
    programs. After you use the DSP ATT (display attributes) function
    to enable visible attribute mode, all attribute characters are
    visible. Attribute characters are characters that appear at the
    start of a field to indicate the following information:

    o  How the field appears on the screen:

       -  At normal intensity

       -  At high intensity

       -  Invisibly

    o  What type of data the application expects in the field:

       -  Numeric

       -  Alphabetic

       -  Alphanumeric