Hello @lingza,
well as lined out, you cannot implement a VertexmMapTag which is the same as a normal VertexMapTag but has extra parameters to realize your desired functionality.
You can solve this problem with either the pattern I described under point 3 in my last posting, or by implementing a ToolData plugin which simply generates the tag. The solution using a driver tag has the advantage that the user can continuously tweak the output of the vertexmap, while a tool must be picked up again.
Actually, I mean that I want to create a tag which contains the vertex weights, then vertex weights are used by ZRemesher after I put the tag into Density Map linkbox.
So I don't need a "vertex map" indeed, but I need a tag I describe above.
This is unfortunately not true. You will need a vertex map tag, as this parameter, the Density Map parameter, will accept only a VertexMapTag. It will not know what to do with a CustomDataTag . I would recommend having a look at the project file I have posted above, it contains a practical example for the pattern of a tag driving a vertex map.
Cheers,
Ferdinand