Please correct me if I'm wrong.. but the metabox builder is limited right?
Both the online builder, as well as the plugin extension version.
What I mean, is that the Builder is not capable of producing the more complex arrays that are needed for certain fields (or nesting).
A couple of simple examples
The HTML field is not available in the builder.
There are other variations on this, where it appears the choices are limited to basic functionality.
That's ok.. but please can someone confirm that this is the case, and if so, then can we safely assume that the builder should really only be used as a shortcut to build out the basic fields, and if we need to extend them with complex conditions then really we need to copy the basic code into a proper template file of some kind?