Datalist tag represent a list of options that represent predefined options for other controls. The <datalist> tag can be used in conjunction with an <input> tag that contains a list of selectable data as a drop down list of input values which contains only legal values. DataList is not visible to the user, but it is associated with the <input> tag through the <input> tag list attribute that takes as its value the id attribute value of the <datalist> tag. The drop down predefined list displays when user enters any value in text field. You can say <datalist> tag provide an auto complete feature on form tags.
HTML5 Event Attributes
When you enter unknown URL you will get an error only on Fire Fox but opera will not show an error and it will navigate you to your specified URL (that you used in action attribute).