NB: More recent documentation for Dyalog APL is available at https://docs.dyalog.com/20.0/.
DyalogLink
This parameter specifies the name of the directory containing the code for Link. The default is [DYALOG]/StartupSession/Link.
Note that Link is required for Session initialisation.
For further information, see https://dyalog.github.io/link/4.0/Usage/Installation.