required attribute code example
Example 1: change input required text html
<input type="text" id="username" required placeholder="Enter Name"
oninvalid="this.setCustomValidity('Enter User Name Here')"
oninput="this.setCustomValidity('')" />
Example 2: C# form required attribute
@Html.TextBoxFor(m => m.ShortName,
new { @class = "form-control", placeholder = "short name", required="required"})