code: public UriTemplateBuilder fragment(VarSpec... var) throws UriTemplateBuilderException
      {
          if (hasExpressionWithOperator(Operator.FRAGMENT))
          {
              throw new UriTemplateBuilderException("The template already has a fragment expression and this would not result in a valid URI");
          }
          addComponent(Expression.fragment(var).build());
          return this;
      }
docs: Appends a template expression using the fragment operator (#) with a
  modifier. The following code:
  <pre>
  import static com.damnhandy.uri.template.UriTemplateBuilder.var;
  
  ...
  
  UriTemplate template =
  UriTemplate.buildFromTemplate("http://example.com/")
  .fragement(var("foo", 1))
  .build();
  </pre>
  Will generate the following URI Template string:
  <pre>
  http://example.com/{#foo:1}
  </pre>
  
  @param var the varspec
  @return the UriTemplateBuilder
  @throws UriTemplateBuilderException if you attempt to add more than one fragment expression, a UriTemplateBuilderException will be raised