From the PHP-Coding_Practices.com site, Tim Koschuetzki has posted an interesting suggestion for developers working with long expressions to make thing simpler - substituting temporary variables for portions of the expression.

Introduce Explaining Variable is particularly useful with long if-statements. You can take each condition, introduce an explaining variable and the conditional logic will read very well. Another occasion is a long algorithm where each step in the calculation can be explained with a well-named temporary variable.

The method is basically the following - declare the temporary variable with part of the expression, replace where needed in the expression, repeat for other parts of the expression. In his example code, he demonstrates its use, pulling out portions of an equation to calculate an item's price to make it much more readable.