marker.js

book.on('renderer:locationChanged', function(locationCfi){
  var epubcfi = new EPUBJS.EpubCFI();
  var doc = book.renderer.doc;
  var mark = document.createElement("a");
  
  // Give the marker an unique id
  mark.id = "look-for-me-1234";
  
  // Add the marker
  epubcfi.addMarker(locationCfi, doc, marker);
  
  // Counter words from start of document
  // Break when you find the marker
  
  // Remove the marker
  epubcfi.removeMarker(mark, doc);
});