Advancing through relative dates with strtotime()
<p>I'm trying to use strtotime() to respond to a button click to advance -1 and +1 days (two buttons) relative to the day advanced to on the previous click.  </p>

<p>Example: It's the 10th of the month, I click "-1 day" button, and now the date reads as the 9th.  I click the "-1 day" button again and now the readout states the 8th day.  I click the "+1 day" button and now the readout states it's the 9th.  </p>

<p>I understand the buttons and the displaying the date, and using $_GET and php to pass info, but how do I get strtotime() to work on the relative date from the last time the time travel script was called.</p>

<p>My work so far has let me show yesterday and today relative to <em>now</em> but not relative to, for example, the day before yesterday, or the day after tomorrow.  Or if I use my "last monday" button, the day before or after whatever that day is.</p>
