Value="#{status.progress}" what's mean?

I found a part of code, like this:
<progress value="#{status.progress}" max="100"></progress>
what’s that mean, why can write like this, Spacebars example didn’t find this.
this is helpers code:

status() {
    let i                = 0;
    const uploads        = _app.uploads.get();
    let progress         = 0;
    const uploadQTY      = Template.instance().uploadQTY;
    let estimateBitrate  = 0;
    let estimateDuration = 0;
    let onPause          = false;

    if (uploads) {
      for (let j = 0; j < uploads.length; j++) {
        onPause = uploads[j].onPause.get();
        progress += uploads[j].progress.get();
        estimateBitrate += uploads[j].estimateSpeed.get();
        estimateDuration += uploads[j].estimateTime.get();
        i++;
      }

      if (i < uploadQTY) {
        progress += 100 * (uploadQTY - i);
      }

      progress         = Math.ceil(progress / uploadQTY);
      estimateBitrate  = filesize(Math.ceil(estimateBitrate / i), { bits: true }) + '/s';
      estimateDuration = (() => {
        const duration = moment.duration(Math.ceil(estimateDuration / i));
        let hours = '' + (duration.hours());
        if (hours.length <= 1) {
          hours = '0' + hours;
        }

        let minutes = '' + (duration.minutes());
        if (minutes.length <= 1) {
          minutes = '0' + minutes;
        }

        let seconds = '' + (duration.seconds());
        if (seconds.length <= 1) {
          seconds = '0' + seconds;
        }
        return hours + ':' + minutes + ':' + seconds;
      })();
    }
    return {
      progress: progress,
      estimateBitrate: estimateBitrate,
      estimateDuration: estimateDuration,
      onPause: onPause
    };
  },

why can’t write like this:
<progress value="{{status.progress}}" max="100"></progress>