usedefaults no yes yes Specifies that the default value defined on a column is to be imported or loaded if the input data file contains no value for that column. Given import data file tabdata.del
usedefaults no yes yes 指定如果输入数据文件没有包含某列的值，就导入或载入该列上所定义的默认值。
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By default, the end-of-file string is an underscore (_); if that character is sent as a single input argument, everything after it is ignored.
As discussed previously, if you don't give a command-line argument, the application will use the default feed sources input XML file (rss_feed_sources.xml).