How to spell: back to front or back on before?
Of course, I want to say that this phrase should always be written as two words, using the adverb Ahead, but in reality everything will depend on context.
In a stable expression Backwards in advance, an adverb is written in advance, which as an adverb will be written together. Similarly, we can give another example: a reverse.
But if you use the noun Before, then the preposition On will be written separately. And to come up with a variant with such a spelling is not difficult: He unexpectedly passed back and drove his ass on the front of my car. Somewhat conversational style, but real.
However, in most cases we write BEFORE.
It is written in one word as it is an adverb, and adverbs with prepositions are written together.