Joshua Thjissen has a post to his site looking at a relatively common operation in PHP code - incrementing values - but gets a lot more in-depth than just a simple overview.

Take a variable, increment it with 1. That sounds like a simple enough job right? Well.. from a PHP developer point of view that might seem the case, but is it really? There are bound to be some catches to it (otherwise we wouldn’t write a blogpost about it). So, there are a few different ways to increment a value, and they MIGHT seem similar, they work and behave differently under the hood of PHP, which can lead to – let’s say – interesting results.

He starts with the most basic situations, updating known integer values, but shows the curious things that can happen when the same operations are done on strings. He digs down into the bytecode that's generated from these bits of code, showing the order of operations when the code is actually executed. He then gets into more detail on each kind of operator, starting with the unary increment operator then moving on to the add assignment expression and add operator. For each he describes the behind the scenes bytcode actions happening and where in the PHP source code its being handled (and how).