id selector can not use

[shuaigeadou]

this place should be undefined,not 'undefined'.
https://github.com/posabsolute/jQuery-printPage-plugin/blob/master/jquery.printPage.js#L69

and when use id selector ,these places are conflict.
https://github.com/posabsolute/jQuery-printPage-plugin/blob/master/jquery.printPage.js#L72
https://github.com/posabsolute/jQuery-printPage-plugin/blob/master/jquery.printPage.js#L74
https://github.com/posabsolute/jQuery-printPage-plugin/blob/master/jquery.printPage.js#L76
https://github.com/posabsolute/jQuery-printPage-plugin/blob/master/jquery.printPage.js#L86
https://github.com/posabsolute/jQuery-printPage-plugin/blob/master/jquery.printPage.js#L87

i'm not good at javascript and can't help fix it.
i use class selector now.

thanks for your open source code at the end.