Undefined variables in a snippet should be highlighted 代码段中的未定义变量应突出显示。
Will be referencing undefined variables 会引用未定义的变量。
Instead of checking for a default compound value , you can also catch the access to an undefined variable 不用再检查默认的复合值,您也可以捕获对未定义变量的访问。
百科解释
An undefined variable in the source code of a computer program is a variable that is accessed in the code but has not been previously declared by that code.