Placeholder

I do not understand exactly how the Default placeholder works. I do not see any documentation on it.

in the old 3.x version, i was able to have the first option in a Select box as a space and then when the form would submit, it would not accept the blank option if it was a required field. How do i set up 4.x to be able to do this? Is this what the default placeholder is for? Thanks.

http://wordpress.org/plugins/si-contact-form/