The core "magic" of the Creative Commons Laser Highlighter Chrome extension (https://chrome.google.com/extensions/detail/iceopjodmdipccjbknbjolkfogkgloei)

content_script.js

// namespaced my implementation of the RDFa
// API using "LinkedData.API" to avoid confusion
// with real (and correcter) implementations.
LinkedData.API.data.setMapping(
    'cc',
    'http://creativecommons.org/ns#');
    
// capture @rel="license"...
var licensedElements = LinkedData.API.getElementsByProperty('license');
// ...and @rel="cc:license"
licensedElements = licensedElements.concat(
    LinkedData.API.getElementsByProperty('cc:license'));
if (licensedElements.length > 0) {
  for (var i = 0, length = licensedElements.length; i < length; i++) {
    var element = licensedElements[i];    
    // no check at all is made with regards to the actual license, so the
    // name "Creative Commons" is a bit misleading, as it highlights any
    // licensed content whatsoever the license might be (although in practice
    // almost all licenses expressed that way seem to be CC ones).
    element.outerHTML =
        '<img id="laser' + i + '" style="position:absolute; left:' + element.x +
        'px; width:' + element.offsetWidth + 'px; height:' +
        element.offsetHeight + 'px; z-index:1000; opacity: 0.8; ' +
        'pointer-events: none; -webkit-transition: opacity 1s linear;" ' +
        'src="' + chrome.extension.getURL("lasers.jpg") + '" />' +
        element.outerHTML;
        
    // the animation (pretty low-tech and ugly, but works)
    var script = document.createElement('script');
    script.innerHTML =
        'var laser' + i + ' = document.getElementById("laser' + i + '"); ' +
        'var interval' + i + ' = window.setInterval(' +
          'function() {' +
            'if (laser' + i + '.style.opacity == 0.8) {' +
              'laser' + i + '.style.opacity = 0.4;' +
            '} else {' +
              'laser' + i + '.style.opacity = 0.8;' +
            '}' +
          '}, 1500);';
    document.body.appendChild(script);    
  }
}