In his latest post Matthias Noback talks about the "dark" side of PHP and some of the common problems of working with and using packages. This is the introduction from his upcoming book on the same subject.

PHP is actually a very problematic language. It has somewhat of a bad reputation. This is no surprise to me, given the huge amounts of bad code written in PHP, produced by novice "developers", yet available for a large audience to copy into their projects. [...] PHP has become such a big player - I guess - because it is so easy to learn. Starting with a simple HTML page it does not take much effort to add some dynamic functionality to it. There is no need to go to school and learn about programming before you can use PHP on your web server.

For all of this good that PHP brings to the table, there's also the bad practices that can come with it. While PHP can be forgiving about bad practices, there's only so far it can go before it starts throwing errors. Since the parsing comes late in the game, bad code can sneak in and not be noticed until it's used.