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In recent years, there has been an increasing tension in the PHP community on how to handle backwards-incompatible language changes. The PHP programming language has evolved somewhat haphazardly and exhibits many behaviors that are considered undesirable from a contemporary position.

Fixing these issues benefits development by making behavior more consistent, more predictable and less bugprone. On the other hand, every backwards-incompatible change to the PHP language may require adjustments in hundreds of millions of lines of existing code. This delays the migration to new PHP versions.

The general solution to this problem is to allow different libraries and applications to keep up with language changes at their own pace, while remaining interoperable. There are quite a few ways in which this general goal can be achieved, which will be discussed in the following.