paste this into any preact app

show-priorities.js

[].filter.call(document.querySelectorAll('*'), el => {
  if (el._component) {
    var p = el._priority = el.offsetHeight ? (1 - el.getBoundingClientRect().top/window.innerHeight) : -1;
    if (p>0) {
      el.setAttribute('data-priority', p);
      return true;
    }
  }
});

var style = document.createElement('style');
style.appendChild(document.createTextNode(`
  [data-priority] {
    position: relative;
  }
  [data-priority]::before {
    content:attr(data-priority);
    position:absolute; left:0; top:0; padding:3px;
    background:orange; color:white;
    font-size: 11px; line-height: 1.2; height:auto;
    z-index: 999;
  }
`));
document.head.appendChild(style);