public UriTemplateBuilder Append(char exprOperator, params VarSpec[] varSpecs)
 {
     var op = Operator.Parse(exprOperator);
     var expression = new Expression(op, new List<VarSpec>(varSpecs));
     components.Add(expression);
     return this;
 }
 public UriTemplateBuilder Append(params VarSpec[] varSpecs)
 {
     var expression = new Expression(Operator.Default, new List<VarSpec>(varSpecs));
     components.Add(expression);
     return this;
 }
 private void CreateExpression()
 {
     var expr = new Expression(exprOperator, varSpecs);
     components.Add(expr);
     varSpecs = null;
 }