“                                                                                                                                                                                                [size=11.000000pt]The function:
                                                [size=10.000000pt]  SCAN(char_var,n,'list-of-delimiters');                                                [size=11.000000pt]returns the [size=11.000000pt]n[size=11.000000pt]th "word" from the char_var, where a "word" is defined as anything between twodelimiters. If there are fewer than [size=11.000000pt]n [size=11.000000pt]words in the character variable, the SCAN function willreturn a blank. If [size=11.000000pt]n [size=11.000000pt]is negative, the scan will proceed from right to left. If [size=11.000000pt]n [size=11.000000pt]is greater than thenumber of words in the string, a missing value is returned.”
[size=11.000000pt]

[size=11.000000pt]请问 什么情况下输出空格，什么情况下输出‘ . ’ missing value
我觉得讲解的是同一种情况啊。谢谢