code: function FocusClock () {
    var blurStart = Date.now()
    var focusStart, focused = false
    var focusTime, blurTime
  
    var clock = h('div', {
      onfocus: function () {
        focusStart = Date.now()
        focused = true
        blurTime = Date.now() - blurStart
        update()
        clock.parentNode.classList.remove('-notify')
      },
      onblur: function () {
        blurStart = Date.now()
        focusTime = Date.now() - focusStart
        focused = false
      }
    },
    'CLOCK'
    )
  
    function update () {
      var page = clock.parentNode
  
      var t = focused
        ? 'focus(focused)'
        : 'focus(blurred)'
      if(page.title != t) page.title = t
  
      if(Date.now() - blurStart > 1000 && !focused && !page.classList.contains('-notify')) {
        page.classList.add('-notify')
      }
  
      if(!focused) return
      clock.innerHTML = ''
      clock.appendChild(
        h('div', [
          h('p', 'current focus:'+(Date.now() - focusStart)),
          h('p', 'blur time:'+blurTime),
          h('p', 'prev focus:'+focusTime)
        ])
      )
    }
  
    setInterval(update, 100)
  
    return clock
  }
docs: clockPage.content === the clock we asked to be added