Follow up to T162127,
Steps to reproduce:
Actual:
You can't as it immediately focuses on <select>
Expected:
I guess it should work.
See the attachment,
That's not the case on Android Chrome or Firefox browser.
But that doesn't matter, as the problem lays in the code appending native form elements to a TextInputWidget. OOUI's TextInputWidget is wrapped in a label element for accessibility reasons and the native select is appended within the TextInput's label, which is an accessibility violation.
You should rather turn the select widget into a DropdownWidget.
And consider turning the TextInput into a NumberInputWidget if it's just about line numbers.
Declining this for code reasons.