当同一个关键字在多个库都存在时，使用时需要加上库名以做区分，否则程序会报错
例如：get element attribute关键字，在XML和Selenium2Library库中都有；
1、不加库名，运行
运行后：报错，
[ WARN ] Keyword 'Get Element Attribute' found both from a custom test library 'Selenium2Library' and a standard library 'XML'. The custom keyword is used. To select explicitly, and to get rid of this warning, use either 'Selenium2Library.Get Element Attribute' or 'XML.Get Element Attribute'.
2、加上库名