$extra argument of form_dropdown

[eluser]Mithun[/eluser]
What is the purpose $extra argument of form_dropdown ?
function form_dropdown($name = '', $options = array(), $selected = array(), $extra = '')

[eluser]jmadsen[/eluser]
http://www.codeignitor.com/user_guide/he...elper.html

If you would like the opening <select> to contain additional data, like an id attribute or JavaScript, you can pass it as a string in the fourth parameter:

[eluser]Mithun[/eluser]
Hard to find the mention of 4th argument there, poor documentation style ;-(
Thank you jmadsen