If there is any such condition in your form that user must enter the first letter as Character and the letters after the first character can be alphanumeric including spaces in the input box. Then you can use the following pattern of the regex.
Regular Expressions are nothing just the pattern against which the values entered by the user in the input boxes is verified at client side or server side.
While registering on many sites, most of the time you will find the website link input field. To validate the link entered by the user at client side, we can use the regular expression. This will elp us in checking the url at server side. Which will save cost, time and money.