Adjacency Constraint allows you to specify when certain elements cannot be built, unless an adjacent element that the former can connect to, has already been completed. This can apply to tunneling, bridges, and complex roof systems.

To use Adjacency Constraint:

• Select required elements and active Adjacency Constraint feature

• Use the to connect dots 
• Control the dot size by Point and Line size
• Use the sign to add/remove start point
• Click on Adjacency Constraint feature again to finish the process

Fore more instructions and  use-cases watch the video below: 

Further Resources

• Supports
• Supports: Automatic Supports and Support as Chain