title: How to define holidays for is.holiday() chron package in R
body: <p>I'm trying to use <code>chron</code>'s <code>is.holiday()</code> function, but I'm having trouble getting it to work.  The documentation says to modify the <code>.Holiday</code> object with the holidays that you wish to use, but the changes I've made to <code>.Holiday</code> don't seem to be detected by <code>is.holiday()</code>.  Could someone provide an example of the appropriate way to load holidays?</p>