Save + export specification

intro

This specification defines a clear separation between saving and export, based on version 2.6.

This change tries to achieve some specific goals:

1. simplify and clarify the user model: what you see on the canvas is always GIMP content;
2. enforce that what is on the canvas is only safe when saved as an xcf file, (or its compressed variants);
3. give primary support for a high-end workflow where the work is saved in xcf, and when it is time for ‘delivery’, it is exported to the required format;
4. give secondary support to workflows where the input and output are the same non-xcf file; the reason for this is not the often touted ‘prosumer photo jpeg–to–jpeg’ workflow, because of GIMP product vision there is no need for optimising this. A much better reason for optimising are situations where high-end GIMP users have to do some quick touch-ups on graphic files for mates or clients, and send them back.

The basic strategy that follows from the points above is: GIMP opens and saves GIMP files and imports/exports the rest. We make however one optimisation: fold Import back into Open, so everything stays (almost) the same there.