Add a default value option to fields that use fetchInput.

[lukecarbis]

It should be possible to set the default value for posts, taxonomies, and users.

[kienstra]

Hi @lukecarbis, Were you thinking of an <select> to choose the post, taxonomy, or user?

For example:

We'll probably have to consider cases with many posts, maybe thousands.

The simplest way to do this would be to accept a post ID in the <input>, but that probably wouldn't be very intuitive.

[lukecarbis]

I guess I was thinking of something similar to what we're showing in the editor. Maybe a select2 or something along those lines?