Q:

Set  value to a non-existent option

I've got a select with options. I need to set the default of the dropdown to a value that is not in the dropdown list. The user can then leave it the same or select a value from the options in the select.
How can this be achieved?
Edit:
This is the scenario: I have a set of data that is normalized. This is fed into the select (as options). After rendering, a value is selected by default. However, sometimes, this value (that has to be selected) might not be in the options - so a good UX would be to still have this shown as the selected option, even if it is not in the normalized data. The user can leave it be or select a "correct" option.

A:

I assume you mean for a placeholder similar to text inputs.  The only way I know of to do this is to make the selected option disabled; however, it must still be an option in the markup.  e.g.

<select>
    <option disabled="" selected="" value="">Select one of the Options Below</option>
    <option>Option 1</option>
    <option>Option 2</option>
    <option>Option 3</option>
</select>

You may be better served by making your own javascript powered one.

