code: func (fb *Firebase) StartAtValue(value interface{}) *Firebase {
  	c := fb.copy()
  	// explicitly not locking here because no one else can
  	// modify this value before we return it.
  	if value != "" {
  		c.params.Set(startAtParam, escapeParameter(value))
  	} else {
  		c.params.Del(startAtParam)
  	}
  	return c
  }
docs: // StartAtValue creates a new Firebase reference with the
  // requested StartAt configuration. The value that is passed in
  // is automatically escaped if it is a string value.
  // Numeric strings are preserved as strings.
  //
  //    StartAtValue(7)        // -> startAt=7
  //    StartAtValue("7")      // -> startAt="7"
  //    StartAtValue("foo")    // -> startAt="foo"
  //    StartAtValue(`"foo"`)  // -> startAt="foo"
  //
  // Reference https://firebase.google.com/docs/database/rest/retrieve-data#section-rest-filtering