What is the error level constant indicating deprecated PHP code?

The error level constant that indicates deprecated PHP code is the E_DEPRECATED constant. This constant is used to signal that a particular feature or functionality in PHP has been deprecated, meaning it is no longer recommended for use and may be removed in future versions. When this constant is triggered, it alerts developers that their code is utilizing a feature that could potentially lead to issues in the future, allowing them to update or replace the deprecated code before it becomes a problem.

This mechanism serves as a useful warning, encouraging developers to adopt updated practices and maintain compatibility with newer versions of PHP. This is particularly important in the context of maintaining codebases, ensuring long-term functionality, and fostering a healthy development environment.

In contrast, the other error level constants serve different purposes: E_WARNING indicates runtime warnings that do not halt the script, E_NOTICE denotes conditioned notices typically about script performance concerns, and E_ERROR signifies serious runtime errors that stop script execution. Thus, E_DEPRECATED specifically targets deprecated code, guiding developers towards better practices.