zend_error() can be used to generate error messages.
    This function accepts two arguments; the first is the error type (see
    zend_errors.h), and the second is the error message. 
    
zend_error(E_WARNING, "This function has been called with empty arguments");  | 
Tabelle 37-1 shows a list of possible values (see 
Abbildung 37-1). These
    values are also referred to in 
php.ini. Depending on
    which error type you choose, your messages will be logged. 
    
Tabelle 37-1. Zend's Predefined Error Messages.
| Error | Description | 
| E_ERROR | 
          Signals an error and terminates execution of the script
          immediately
          . | 
| E_WARNING | 
          Signals a generic warning. Execution continues.
          | 
| E_PARSE | 
          Signals a parser error. Execution continues.
          | 
| E_NOTICE | 
          Signals a notice. Execution continues. Note that by
          default the display of this type of error messages is turned off in
          php.ini.
          | 
| E_CORE_ERROR | 
          Internal error by the core; shouldn't be used by
          user-written modules.
          | 
| E_COMPILE_ERROR | 
          Internal error by the compiler; shouldn't be used by
          user-written modules.
          | 
| E_COMPILE_WARNING | 
          Internal warning by the compiler; shouldn't be used by
          user-written modules.
          |