<style>
.max1:invalid {
color: red }
.max1:valid {
color: black;}</style>
<body>
<select name="CanFrame_Type" id="CanFrame_Type" onchange='document.getElementById("Can_ID").pattern=this.value'>
<option value="[0-7][A-F\d]{2}|[A-F\d]{1,2}">Std</option>
<option value="[8-9A-F][A-F\d]{2}|[A-F\D]{4,8}">Ext</option>
</select>
<input id="Can_ID" name="Can_ID" size="5" class="max1" pattern="[A-F\d]{1,5}" />
</body>