I have a custom theme, which has been forked from the “Plain” theme, but apparently from a version before the “Show at the top of printed documents” option was added to Custom Fields; as a result, my Custom Field is always showing at the bottom of the document. I am guessing that there is something like a top_of_document property on the custom_fields items, but I cannot find any reference for the Theme customisation types/properties, and I cannot seem to get to the source of the latest “Plain” theme in order to try copy from it.
Where could I find a reference for the Theme customisation types/properties, or the source of the latest “Plain” theme?