Roslyn - SyntaxRewriter to remove region directives

CSharpRemoveRegionRewriter.cs

public class CSharpRemoveRegionRewriter : SyntaxRewriter
{
  public CSharpRemoveRegionRewriter()
    : base(true)
  {
  }

  public override SyntaxNode VisitRegionDirectiveTrivia(RegionDirectiveTriviaSyntax node)
  {
    return Syntax.SkippedTokensTrivia();
  }

  public override SyntaxNode VisitEndRegionDirectiveTrivia(EndRegionDirectiveTriviaSyntax node)
  {
    return Syntax.SkippedTokensTrivia();
  }
}

VbRemoveRegionRewriter.cs

public class VbRemoveRegionRewriter : SyntaxRewriter
{
  public VbRemoveRegionRewriter()
    : base(true)
  {
  }
  
  public override SyntaxTrivia VisitTrivia(SyntaxTrivia trivia)
  {
    var updatedTrivia = base.VisitTrivia(trivia);
    var directiveTrivia = trivia.GetStructure() as DirectiveTriviaSyntax;
    if (directiveTrivia != null)
    {
      if (directiveTrivia.Kind == SyntaxKind.DirectiveTrivia)
      {
        if (directiveTrivia.Directive.Kind == SyntaxKind.RegionDirective ||
            directiveTrivia.Directive.Kind == SyntaxKind.EndRegionDirective)
        {
          updatedTrivia = default(SyntaxTrivia);   
        }
      }
    }
    return updatedTrivia;
  }
}

there aren't any usings on these files, Can you tell me where Syntax.SkippedTokensTrivia is?

@ImaginaryDevelopment apparently, the SyntaxFactory was once called Syntax. The method SkippedTokensTrivia exists in the SyntaxFactory class.