Autocomplete UI, highlight multiple words in tags

I wish this helpful for you rails3-jquery-autocomplete plugin? It seems that it doesn't support multiple autocomplete, you need to modify the plugin code!! If you insist on your former ideas, follow my steps.
run bundle show rails3-jquery-autocomplete to get the plugin working directroy mate /lib/autocomplete.rb

define_method("autocomplete_#{object}_#{method}") do
  arr = params[:term].split(",")
  unless params[:term] && params[:term].empty?
    items = object.to_s.camelize.constantize.where(["LOWER(#{method}) LIKE ?", "#{arr[arr.size-1]}%"]).limit(limit).order(order)
  else
    items = {}
end

render :json => json_for_autocomplete(items, method)

To fix this issue It seems to me you should overwrite the _renderItem method to have custom rendering of the items. The code could be about the following:

$("#studentName").autocomplete({/* all your parameters*/})
    .data("autocomplete")._renderItem = function (ul, item) {
        var newText = String(item.value).replace(
                new RegExp(this.term, "gi"),
                "<span class='ui-state-highlight'>$&</span>");

        return $("<li></li>")
            .data("item.autocomplete", item)
            .append("<div>" + newText + "</div>")
            .appendTo(ul);
    };

var $elem = $("#studentName").autocomplete({/* all your parameters*/}),
    elemAutocomplete = $elem.data("ui-autocomplete") || $elem.data("autocomplete");
if (elemAutocomplete) {
    elemAutocomplete._renderItem = function (ul, item) {
        var newText = String(item.value).replace(
                new RegExp(this.term, "gi"),
                "<span class='ui-state-highlight'>$&</span>");

        return $("<li></li>")
            .data("item.autocomplete", item)
            .append("<div>" + newText + "</div>")
            .appendTo(ul);
    };
}

Hope this helps I want to replace HTML template content with new one after highlighting the words those match the search input. , Firstly I am sorry for quick tested answer.
Here is your answers:

var reg = new RegExp("[\>][^\<\>.]*"+tag+"[^\<\>.][\<]*","gi");

var reg = new RegExp("[\>][^\<\>.]*"+tag+"[^\<\>.]*[\<]*","gi");

var text = "<div>fireman has killed fire</div>";

text = "<div><highlight>fire</highlight>man has killed <highlight>fire</highlight></div>";

Any of those help The only way I can think of is to use getBoundingClientRect() and draw an overlay over the box while the user is writting.
getBoundingClientRect() is expensive, but running at user typing speed is no problem actually.