此函式用在设定变数的预设值，如果变数的值是空白或尚未设定的话，则会列印出预设值，使用此函式时会预设需要一个参数。
This is used to set a default value for a variable. If the variable is empty or unset, the given default value is printed instead. Default takes one argument.
设定区域变数签章，描述关联之动态方法的区域变数配置。
Sets the local variable signature that describes the layout of local variables for the associated dynamic method.
如果对区域变数设定资料中断点，最好的做法是在函式结束前移除或停用中断点。
If you set a data breakpoint on a local variable, the best practice is to remove or disable the breakpoint before the function ends.
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