It would be very helpful to be able to require that input into a free text assignment submission or free text entry in a quiz match a regular expression - not for checking the correct answer, but so that a student enters a valid attempt at an answer. For example, currently a numerical blank in a quiz will not allow students to enter letters. With this option, a fill in the blank question + regular expression could behave similarly, for more than only numerical fields - students could not enter numbers, multiple words, or accidentally copy in html tags when a blank or assignment submission requires a single alphabetic word (specified by a regular expression). This would also discourage students from entering full names when usernames are requested and similar errors. It would enable the assignment turn in to better validate many types of submissions - commit IDs, specific types of URLs, single words, etc.