A new PNG spec

That is not backward compatible problem. If a cable that does 100w charging when using pd2.0, but only 60w when using with pd3.1 device, then i would agree with you.

The problem is not backward compatibility but labeling. A USB-C cable looks universal but isn’t. Some of them just charge, some do data, some do PD, some give you access to high speed. But there is no way to know.

I believe the problem here is that you will have PNG images that “look” like you can open them but can’t.

the parent said "changing the compression algorithm will break backwards compatibility", which i assume is something works now won't work in the future. The usb-c spec is intentionally trying to avoid that.

Cable labeling could fix 99% of the issues with USB-C compat. The solution should never be blaming consumer for buying the wrong cable. Crappy two-wire charge-only cables are perfectly fine for something like a night desk lamp. Keep the poor cables, they are okay, just tell me if that's the case.

Some aren't even USB. Thunderbolt and DisplayPort both use USB-C too.

Today, I can save a PNG file off a random website and then open it.

If PNG gets extended, it's entirely plausible that someone will view a PNG in their browser, save it, and then not be able to open the file they just saved.

There are those who claim "backwards compatibility" doesn't cover "how you use it" - but roughly none of the people who now have to deal with broken software care about such semantic arguments. It used to work, and now it doesn't.

That's not just an issue with usb-c. normal usb a and b cables can have data or no data depending on how stingy the company wants to be, and you can't know until you test it

This is what I fear, too.

Do they mention which C libraries use this spec?

Same thing with PNG. Just call the format with new additions it PNGX, so the user can clearly see that the reason their software can’t display the image is not a file corruption.

This is just pretending that if you have a cat and a dog in two bags and you call it “a bag”, it’s one and the same thing…

which is what usb-c spec has been avoiding so far. Even in USB4 spec, there are a lot of mentioning the new spec should be compatible with TB3 devices.

USB-C spec is anything but breaking backward compatible.

> Cable labeling could fix 99% of the issues with USB-C compat.

Labelling is a poor band-aid on the root problem - consumer cables which look identical and fit identically should work wherever they fit.

There should never have been a power-only spec for USB-C socket dimensions.

If a cable supports both power and data, it must fit in all sockets. If a cable supports only power it must not fit into a power and data socket. If a cable supports only data, it should not fit into a power and data socket.

It is possible to have designed the sockets under these constraints, with the caveat that they only go in one way. I feel that that would have been a better trade-off. Making them reversible means that you cannot have a design which enforces cable type.

The alternative is the website operator who wants to save on bandwidth instead adopts JXL or WEBP or what have you and ... the end user with old software still can't open it.

It's a dichotomy. Either the provider accommodates users with older software or not. The file extension or internal headers don't change that reality.

Another example, new versions of PDF can adopt all the bells and whistles in the world but I will still be saving anything intended to be long lived as 1/a which means I don't get to use any of those features.

You can get pretty good guesses just by feel and length. Tiny with a super thin cable? Probably charge only.

Thunderbolt meets usbc specs (and exceeds them afaik), so it is still usb...

So since my vape (example, i dont vape) has a power and data slot for charging and firmware updates, i should be limited to only using dual purpose cables day to day rather than a power only cable?

> If a cable supports only power it must not fit into a power and data socket

That's even more confusing than the current state of affairs. If my phone has power and data socket, then I cannot use power only cable to only charge it? Presumably with the charger that has power only socket. So I need a cable with two different ends anyway. Just go micro-USB at this point :)

Funnily enough, there is a 100% overkill way to solve such issues. Just use super expensive certified TB cables. Well... plus a A-to-C adapter for noncompliant devices, I guess.

> So since my vape (example, i dont vape) has a power and data slot for charging and firmware updates, i should be limited to only using dual purpose cables day to day rather than a power only cable?

Well, yes.

Why can't you use a power+data cable for the vape (or whichever appliance takes both)? What's the deal-breaker here?

The alternative is labeling, or plugging cables in to see if they do what you want them to do.

Both are a poor user interface.

Two wire cables are not in the specification, just like A-to-A cables aren't. The whole charging above 100mA with resistor hacks wasn't in the standard either until they had to grandfather it in. The implementers forum isn't responsible for non-members breaking their spec.

Is the same true for my laptop? Or soldering plate? Both take over 150w of power. Buying a power and data cable is expensive compared to just power, and the length of cable is severely limited...or the data speed impaired significantly. How slow does the data have to be for it to be non compliant?