Abstract the required fields/attributes of imported content, and their validators ( ie: is_numeric/is_email )

Having a list of fields/attributes that must exist within an imported item as a class member, with a built-in method to check them, and possibly validate them via a defined function ( ie: is_numeric / is_email ), can speed up development time and cut down on the lines to be wrote for this simple functionality.

The issue names no files, tests, or entry points. Start by reviewing how imported items currently define required fields and validation in the PHP/WordPress migration framework; done should mean a documented design and implementation path for shared required-field checks and validators such as is_numeric or is_email.

Written by the indexing model from the issue text.