code: public WebTarget matrixParam(String name, Object... values) {
          final UriBuilder copy = cloneUriBuilder();
          copy.matrixParam(name, values);
          return newWebTarget(copy);
      }
docs: Create a new WebTarget instance by appending a matrix parameter to the existing set of matrix parameters of the
  current final segment of the URI of the current target instance. If multiple values are supplied the parameter
  will be added once per value.
  <p/>
  Note that the matrix parameters are tied to a particular path segment; appending a value to an existing matrix
  parameter name will not affect the position of the matrix parameter in the URI path.
  <p/>
  A snapshot of the present configuration of the current (parent) target instance is taken and is inherited by the
  newly constructed (child) target instance.
  
  @param name    the matrix parameter name, may contain URI template parameters.
  @param values  the query parameter value(s), each object will be converted to a {@code String} using its
  {@code toString()} method. Stringified values may contain URI template parameters.
  
  @return  a new target instance.