Q:

HTML Javascript <%= %> tag

While looking through a jquery plugin's source code on github, I stumbled upon a weird usage of  the <%= %> tag. I am aware that erb uttilizes those tags to execute ruby code within an HTML document, but I had never seen that used in javascript. As far as I can see, the tags are used in the same context as in erb, but instead execute Javascript code. How do those tags work and where can I find more information about them? 
Example code:
</div>
 <div class="clndr-grid">
  <div class="days-of-the-week">
    <% _.each(daysOfTheWeek, function(day) { %>
      <div class="header-day"><%= day %></div>
    <% }); %>
    <div class="days">
      <% _.each(days, function(day) { %>
        <div class="<%= day.classes %>"><%= day.day %></div>
      <% }); %>
    </div>
  </div>
 </div>
</div>

A:

This is using underscore.js, especially the template function of the library:
More infomation here:
http://underscorejs.org/#template

