Thanks for the question - I will take each in turn.
>> Marker Data values have no influence on parameters for Geometry Offsets.
Yes, I'm afraid this isn't really what markers are designed for. For example, you could have multiple makers on a spline each with different data, in that case RailClone would not know which marker's data to use. The Generator's rules, including offsets, apply to the whole of each spline attached to the generator. At present you cannot change them mid spline I'm afraid. Instead, you could do this using the Transform operator.
>> Example 1 - Using markers at position 0
It seems you have solved this one already by adding a Null segment to the Marker's input, but it relates to the explanation in the second example....
>> Example 2 - Marker replaces start segment
The marker will indeed overwrite the geometry in the start segment. This is because Markers can not occupy exactly the same position as other markers, vertices, evenly segments, the start, or the end. Internally the spline is divided by all these inputs, and you cannot divide the same position twice. When evaluating spline divisions that occupy the same position, the order is as follows: Evenly, Corner, Start, End, Marker. As you can see - marker overwrites all other types.
If you do need geometry in exactly the same place as another input, one solution would be to use another generator.
>> Example 3 - Marker Data not working on the second generator.
This is because of the way you have written the expressions. To access the marker data you have used the dot syntax used to specify a specific generator:
The A refers to the generator's name, so it won't work on another generator. This syntax is intended for use with nested generators for when you need to specify which one you wish to access the data from. In this case though, there is no nesting so you can simply use:
And it will work with every generator to which it is attached.
I hope that all makes sense, please let me know if you have any further questions.
All the best,