Final answer:
To specify a date format such as mm/dd/yyyy in an HTML5 form, use the element with the type attribute set to 'date' and consider additional JavaScript for strict format enforcement.
Step-by-step explanation:
To require users to enter a date in a specific format such as mm/dd/yyyy in an HTML5 form, you would use the <input> element with the type attribute set to 'date'. Browsers that support HTML5 will typically provide a date picker to help users enter a valid date, which ensures the format is as specified. However, to strictly enforce the mm/dd/yyyy format without any variation, additional JavaScript validation might be required, as the HTML5 date picker may produce different date formats based on the user's locale settings.