title: ICS calendar feed with Quarterly recurring events
body: <p>I am working on a ICS calendar feed that will be consumed by different calendar apps. I am using PHP iCal package to generate the feed : <a href="https://github.com/markuspoerschke/iCal" rel="nofollow noreferrer">https://github.com/markuspoerschke/iCal</a></p>
  <p>The base system what provides me data for ics feed, has following types of  recurring events:</p>
  <blockquote>
  <p>Daily, Weekly, Monthly, Quarterly, Yearly</p>
  </blockquote>
  <p>I was looking through RFC doc for this standard <a href="https://www.rfc-editor.org/rfc/rfc5545" rel="nofollow noreferrer">https://www.rfc-editor.org/rfc/rfc5545</a>, and standard support only following repeat frequencies:</p>
  <pre><code>   freq        = &quot;SECONDLY&quot; / &quot;MINUTELY&quot; / &quot;HOURLY&quot; / &quot;DAILY&quot;
                 / &quot;WEEKLY&quot; / &quot;MONTHLY&quot; / &quot;YEARLY&quot;
  </code></pre>
  <p>that means no standard way to have a quarterly recurring event.</p>
  <p>One solution that I have in mind is to add a new event after every 3 month. However, this will add 4 separate events in a year, and not 4 recurring instance of original event added.</p>
  <p>Is there a way to 'trick' ics to create quarterly 'recurring' events?</p>