PHP Error Levels

There are sixteen different error levels (i.e. types) are available in PHP.

## Error Levels in PHP
Usually, whenever the PHP engine encounters a problem that prevents a script from running properly it generate an error message. There are sixteen different error levels and each level is represented by an integer value and an associated constant. Here's a list of error levels:

| Error Level         | Value | Description                      |
|---------------------|-------|------------------------------------|
| E_ERROR             | 1     | A fatal run-time error, that can't be recovered from. The execution of the script is stopped immediately. |
| E_WARNING           | 2     | A run-time warning. It is non-fatal and most errors tend to fall into this category. The execution of the script is not stopped. |
| E_PARSE             | 4     | The compile-time parse error. Parse errors should only be generated by the parser. |
| E_NOTICE            | 8     | A run-time notice indicating that the script encountered something that could possibly an error, although the situation could also occur when running a script normally. |
| E_CORE_ERROR        | 16    | A fatal error that occur during the PHP's engine initial startup. This is like an E_ERROR, except it is generated by the core of PHP. |
| E_CORE_WARNING      | 32    | A non-fatal error that occur during the PHP's engine initial startup. This is like an E_WARNING, except it is generated by the core of PHP. |
| E_COMPILE_ERROR     | 64    | A fatal error that occur while the script was being compiled. This is like an E_ERROR, except it is generated by the Zend Scripting Engine. |
| E_COMPILE_WARNING   | 128   | A non-fatal error occur while the script was being compiled. This is like an E_WARNING, except it is generated by the Zend Scripting Engine. |
| E_USER_ERROR        | 256   | A fatal user-generated error message. This is like an E_ERROR, except it is generated by the PHP code using the function trigger_error() rather than the PHP engine. |
| E_USER_WARNING      | 512   | A non-fatal user-generated warning message. This is like an E_WARNING, except it is generated by the PHP code using the function trigger_error() rather than the PHP engine |
| E_USER_NOTICE       | 1024  | A user-generated notice message. This is like an E_NOTICE, except it is generated by the PHP code using the function trigger_error() rather than the PHP engine. |
| E_STRICT            | 2048  | Not strictly an error, but triggered whenever PHP encounters code that could lead to problems or forward incompatibilities |
| E_RECOVERABLE_ERROR | 4096  | A catchable fatal error. Although the error was fatal, it did not leave the PHP engine in an unstable state. If the error is not caught by a user defined error handler (see set_error_handler()), the application aborts as it was an E_ERROR. |
| E_DEPRECATED        | 8192  | A run-time notice indicating that the code will not work in future versions of PHP |
| E_USER_DEPRECATED   | 16384 | A user-generated warning message. This is like an E_DEPRECATED, except it is generated by the PHP code using the function trigger_error() rather than the PHP engine. |
| E_ALL               | 32767 | All errors and warnings, except of level E_STRICT prior to PHP 5.4.0. |