I have a menu on the left side which is in a div tag, wondering how I can have the div tag move up or down the page as people scroll.
So I want the menu to constantly stay in the same area as people move about the page.
Explain concepts important to validation of email addresses with regular expressions. Applies to most languages/tools that uses regular expressions.
Consider email address RFCs:
Look at HTML5 form input element (with type=email) regex pattern: