Platform English handles the nuances of everyday communication better and accommodates both spoken and written uses of language, unlike pairings such as formal/informal and standard/nonstandard.
Most handbooks take note of different varieties (or registers) of English and sort them into formal and informal. The opposition is usually based on perceived differences in the occasions for using one or the other.
In this scheme, a given rhetorical situation either calls for formal English, generally assumed to have more stringent requirements, or else it will tolerate the “looser” rules of informal English. In a sense, handbooks are compilations of the rules of formal English, famously numerous and difficult to learn, which allow writers to find what they need when faced with one of these formal rhetorical situations.
But times change. Can an e-mail be formal? What about a Twitter post--should you edit for grammar? After all, if you're trending, the whole world is watching!