> Although standard English is usually associated with official communications and settings, it is diverse in registers (stylistic levels), such as those for journalism (print, television, internet) and for academic publishing (monographs, academic papers, internet). This diversity in registers also exists between the spoken and the written forms of SE, which are characterised by degrees of formality; therefore, Standard English is distinct from formal English, because it features stylistic variations, ranging from casual to formal
If there is such a thing as Standard English, then it would allow phrases like “amn’t”, according to this definition anyway, as a casual style or register.
Evidently, it is usable to all speakers - you can come up with it yourself for the first time ever, and still be perfectly understood by every other speaker who hears it for the first time.
