I had this question come up today that I thought worth covering.
The Question was if I have two lines that intersect at a common location and common elevation, how do I create that using the vertical design tool?
The problem being raised is that if I simply create an Elevation Instruction at the end point of the lines where they meet, that the vertical design sees that as an ambiguous solution  i.e. which line are you applying the elevation to? because there are 2 or more options at that location.
There are currently 2 potential solutions to the problem that I have covered in this short video

Apply two separate elevation rules, one to each line very close to the end points of the lines, but not at the end point. Zoom right in to the end point and you will see that 1 grid is 0.001’ and you can place the elevation instruction using the Near Point snap anywhere within a Grid distance of the corner where the lines meet i.e. at 0.0002’ for example. Repeat for the second line. Now you will have matching elevations, no surface flags, and a perfect model. The very small flat spot in the corner is way smaller than anything you can build on site.

Use the Connector Instruction type to connect from Line 2 to Line 1 or vice versa. This matches the elevation of the second line to that of the first at the location where the two lines meet or cross. If you need to elevate Line 1 at the corner then you can do that using an Elevation Instruction as above very close to the corner itself.
The video below shows how to do this in both scenarios
Hope that this answers the question
Alan