When this value is set to a non-null-value it's value is used as php's error_reporting-level inside of display() and fetch(). When debugging is enabled this value is ignored and the error-level is left untouched.
當此變數設定為非空值（non-null-value）時則此變數的值在 display() 與 fetch() 函數內會被當成 php 的 error_reporting_level 使用。當除錯開啟時此數值會被忽略 且不會使用 error-level。