Worlds Edge was originally an epic-length PGP that I started writing some years back and then lost hold of. A lot of my writing goes that way; apparently watertight plots somehow work their way loose and end up becoming unwritable. No matter; the PGP might have fallen by the wayside, but its obvious continuity with some of the stories I had finished meant that I could happily use the PGP title as a blanket reference for the finished product.
When I describe Worlds Edge as a 'subcanon', I basically mean this; it's a body of material - fiction and non-fiction, published or otherwise - that builds on, elaborates and rationalises the aired series (the 'primary canon'). As far as is practicable, the primary canon is taken 'as broadcast'; events, spoken words, and other factual material are used as a starting point. However, the primary canon is not entirely immutable. There are a number of anomalies and inconsistencies in the series, and one purpose of a subcanon is to either resolve these, or to select the 'best fit' option out of the mutually irreconcilable alternatives. In a very few cases, the primary canon is deemed to be just plain wrong when it becomes next to impossible to squeeze into the wider-ranging rationalisation.
A subcanon is also a very subjective interpretation of the primary canon. It selects, filters, re-edits and transmutes the raw material of the primary canon into a particular format. The primary canon becomes the raw material from which the subcanon is fashioned, and so becomes not what 'really' happened, but a representation of what really happened. (If this seems to be taking a few liberties with the aired programmes, bear in mind that virtually all viewers do this as a matter of routine. If we see a dodgy special effect, for instance, we charitably reinterpret it so we see what we think we should have seen, not what we actually do see. Or do you really think the pursuit ships wobble into attack on their piano wires?)
In most cases, the Worlds Edge subcanon does not stray significantly from what was said and done in the series. It does not, however, acknowledge the canonicity of Dawn of the Gods.
It should also go without saying that this interpretation of the B7 universe is solely my own, with no intention of pushing it as in any way official or authoritative.
The following stories of mine are part of the Worlds Edge subcanon, in chronological order (that is, the order in which they happen, not in which they were written or published):
The jury's still out on Comitted (The Way Back) and The Last Waltz (Stadler Link) - both are PGPs, and either or both might become part of the subcanon if I ever find the nerve and stamina to attempt another PGP.
A number of other subcanonical stories are 'under development', which means I started them, lost the thread, and put them aside, but might one day go back to them.
The Worlds Edge Timeline - the events in the aired series placed into a wider historical context.
A Worlds Edge Glossary - mainly things mentioned in my fiction.
Ship Speed and Spacials - if you can't fiddle the physics, invent it from scratch.
Comments, suggestions (or violent disagreements, for that matter) are welcome, should you feel the urge. Feel free to e-mail me.