title: is it possible to display number of week in row with selected week?
body: <p>is it possible to display number of week in row with selected week or in toolbar?</p>
  
  <p>I tried to use ToolbarComponent, but it override all header. But I want to keet it the same as it's just to add information about selected week</p>
  
  <pre><code>class CustomElements extends PureComponent {
    renderWrappedWeekDay = (date, selectedDate, dayInCurrentMonth) =&gt; {
      const { classes } = this.props;
  
      let dateClone = date.clone();
      let selectedDateClone = selectedDate.clone();
  
      const start = selectedDateClone.startOf("week").toDate();
      const end = selectedDateClone.endOf("week").toDate();
  
      const dayIsBetween = dateClone.isBetween(start, end, null, []);
      const isFirstDay = dateClone.isSame(start, "day");
      const isLastDay = dateClone.isSame(end, "day");
  
      const wrapperClassName = clsx({
        [classes.highlight]: dayIsBetween,
        [classes.firstHighlight]: isFirstDay,
        [classes.endHighlight]: isLastDay
      });
  
      const dayClassName = clsx(classes.day, {
        [classes.nonCurrentMonthDay]: !dayInCurrentMonth,
        [classes.highlightNonCurrentMonthDay]: !dayInCurrentMonth &amp;&amp; dayIsBetween
      });
  
      return (
        &lt;div className={wrapperClassName}&gt;
          &lt;IconButton className={dayClassName}&gt;
            &lt;span&gt;{dateClone.format("DD")} &lt;/span&gt;
          &lt;/IconButton&gt;
        &lt;/div&gt;
      );
    };
  
    render() {
      const { selectedDate } = this.state;
  
      return (
        &lt;DatePicker
          label="Week picker"
          value={selectedDate}
          onChange={this.handleWeekChange}
          renderDay={this.renderWrappedWeekDay}
          labelFunc={this.formatWeekSelectLabel}
        /&gt;
      );
    }
  }
  </code></pre>
  
  <p>example <a href="https://codesandbox.io/s/week-picker-36ig1" rel="nofollow noreferrer">https://codesandbox.io/s/week-picker-36ig1</a></p>