I think the spirit of the RFC is mostly about complications arising if such headers ever became standardized, but also that the "X-" just doesn't add any value – it's a convention without a purpose and just makes headers longer. In fact, it arguably becomes less useful the more people use it.
So I think it's better for new projects to drop the "X-".
On the other hand, I think it's reasonable to prepend with "HX-" because these headers apply to functionality that is specifically related to the capabilities of this library (or similar libs). It is highly improbable that this syntax would ever become standardized in either the HTML or HTTP specs, but if it did, the HX in front of headers makes sense given that the tag attributes are also prepended with an HX.
From an entirely stylistic perspective, I also think that shoving an "X-" in front of all your headers is ugly (ugliness can of course be justified by usefulness, but as stated above I don't think that applies here).
But of course these are just my thoughts on the matter, others might like "X-", though I'll admit I don't know why you would.
So I think it's better for new projects to drop the "X-".
On the other hand, I think it's reasonable to prepend with "HX-" because these headers apply to functionality that is specifically related to the capabilities of this library (or similar libs). It is highly improbable that this syntax would ever become standardized in either the HTML or HTTP specs, but if it did, the HX in front of headers makes sense given that the tag attributes are also prepended with an HX.
From an entirely stylistic perspective, I also think that shoving an "X-" in front of all your headers is ugly (ugliness can of course be justified by usefulness, but as stated above I don't think that applies here).
But of course these are just my thoughts on the matter, others might like "X-", though I'll admit I don't know why you would.