Original
Default parameters in forward and interface declarations
If a routine has a forward declaration or appears in the interface section of a unit, default parameter values; if there are any must be specified in the forward or interface declaration. In this case, the default values can be omitted from the defining (implementation) declaration; but if the defining declaration includes default values, they must match those in the forward or interface declaration exactly.
See also
Forward and interface declarations
译文
向前声明和接口声明中的缺省参数
如果一个例程有一个forward声明或出现在单元的接口节，并且缺省参数在其forward声明或接口声明中被指定。这种情况下，在相应的定义（实现）声明中，缺省值可以被忽略（即不必重申）；但如果定义声明包括缺省值，则必需与相应的向前（forward）声明或接口声明严格匹配。