Sorting of usings with underscore differs from Visual Studio

[RudyMauro-Datamind]

Input:

using Api.Repositories._Core;
using Api.Repositories.Helpers;

Output:

using Api.Repositories.Helpers;
using Api.Repositories._Core;

Expected behavior:
It should match the behavior of Visual Studio's "Sort usings"

using Api.Repositories._Core;
using Api.Repositories.Helpers;

[seoj-trifork]

Are there some docs about sorting using? I was looking for a tool that does this, I didn't know Csharpier did it because I couldn't find it in the docs.