function searchSubstr( fullText, searchText, allowOverlap ){
  if(!searchText){return 0;}
  var regex = new RegExp(searchText, 'igm'), count=0, substr;
  while(substr=regex.exec(fullText)){
     count++;
    if(allowOverlap!==false){
      regex.lastIndex -= Math.ceil(substr.length/2);
    }
  }
  return count;
}