Added support for configurable user-supplied Jinja HTML templates for the notebook. Paths to directories containing template files can be specified via NotebookApp.extra_template_paths. User-supplied template directories searched first by the notebook, making it possible to replace existing templates with your own files.

For example, to replace the notebook's built-in error.html with your own, create a directory like /home/my_templates and put your override template at /home/my_templates/error.html. To start the notebook with your custom error page enabled, you would run:

ipython notebook '--extra_template_paths=["/home/my_templates/"]'

It's also possible to override a template while also inheriting from that template, by prepending templates/ to the {% extends %} target of your child template. This is useful when you only want to override a specific block of a template. For example, to add additional CSS to the built-in error.html, you might create an override that looks like:

{% extends "templates/error.html" %}

{% block stylesheet %}
{{super()}}
<style type="text/css">
  /* My Awesome CSS */
</style>
{% endblock %}