Help! My design package/theme is’nt showing up

So Magento is this great big system that comes with a lot of options. One of these options is to change the appereance of each part of your webshop, and even to do so conditionally.

However sometimes you can’t see the forest for the trees, especially when working on a shop that is not your own. So sometimes your fancy new design package/theme/skin does not show up… You uploaded your files to /app/design and /skin. Set the new package in the backend configuration… But nothing changes… Why?!

So were to look?
1. System -> Designs: Yes! Not the design section of your system configuration, but the one in the dropdown under configuration. It allows you to set designs specifying dates when to show this design. This one is easy to overlook…
2. System -> Configuration -> Design: This is where you normally specify the design package. And all may seem well at a first glance…
but….
2.1. Check the exceptions! Magento allows you to specify exceptions… Perhaps one of these is blocking your new package.
2.2. Be sure to check the different configuration scopes… The design package can also be specified at a website of storeview level… Check all of them! And check their exceptions…
3. Specific content: Well if all the above is fine… Perhaps specific content is failing. Magento allows you to specify a different design at a category / product / page level. So check the design tab of you CMS Pages (start at your homepage), products and categories. Imagine changing the package, and the homepage has a specific design specified… Pressing F5… Flushing cache… Checking mod_expires… Browser cache… ;-).