Delegate input for validation is sometimes visible & may receive focus

[rnicholus]

In #19, a "dummy" input was created when form validation is required to ensure the (ajax-)form prevents submission if file-input is invalid. This is created as a 0x0 opaque text input, but may take up space in some cases. For example, if bootstrap's CSS file is imported, the input will include padding and a border.

The input also does not contain a negative tabindex value, so it may receive focus (it shouldn't).