ok..so instead of x- ..what should we be using for none standard header?
employ meaningful but currently unused names
Not pretty for those who like certainty and formality, but very in tune with how things can work with global search.
"4. SHOULD identify a convention to allow local or implementation-specific extensions, and reserve delimeters for such uses as needed."
As has been mentioned by another commenter[0] these parts invite the drawing of parallels to CSS vendor prefixes.
e.g. -moz-/-ms-/etc...