Search is performed on every field keyup event, via ajax calling of search.json file where target fields are collected for every post:

{
  "title"     : "{{ post.title }}",
  "url"       : "{{ post.url }}",
  "date"      : "{{ post.date | date: "%e %B %Y" }}",
  "tags"      : "{% for tags in post.tags %}{{ tags }}{% if forloop.last %}{% else %}, {% endif %}{% endfor %}",
  "excerpt"   : "{{ post.excerpt | strip_html }}",
  "category"  : "{{ post.category }}"
}

Search results div is populated by template setting variabile in assets/js/simpleJekyllSearch.js which is now set like _includes/archive-item.html.

You can pass query string to search page as url parameter so you can careate filter links like /search/?string=specific-tag or /search/?string=genuary 2014.

Customize search

• If you need to restrict search on custom post fields just add them in post front-matter:

---
layout: post
title: my title
customkey: yellow
---

• Add in pages/search.json a call "customkey" : "{{ post.customkey }}"

• You can show custom keys on search results tweaking template var in assets/js/simpleJekyllSearch.js using {customkey}.