Use set_placeholder to set placeholder text for an input element.
$dbForm = new C_DatabaseForm("SELECT * FROM Employees", "EmployeeID", "Employees");
$dbForm -> set_label("EmployeeID", "Employee ID");
$dbForm -> set_label("LastName", "Last Name");
$dbForm -> set_label("FirstName", "First Name");
$dbForm -> set_label("BirthDay", "DOB");
$dbForm -> set_hide("Extension");
$dbForm -> set_hide("hireDate");
$dbForm -> set_placeholder('Title', 'official job title');
$dbForm -> display();
$dbForm -> set_label("EmployeeID", "Employee ID");
$dbForm -> set_label("LastName", "Last Name");
$dbForm -> set_label("FirstName", "First Name");
$dbForm -> set_label("BirthDay", "DOB");
$dbForm -> set_hide("Extension");
$dbForm -> set_hide("hireDate");
$dbForm -> set_placeholder('Title', 'official job title');
$dbForm -> display();