Complex sentence: The project was to be the foundation of "A Comprehensive Grammar of the English Language", a widely used reference grammar and the first of English in real use rather than being structured by rules handed down from Greek and Latin models.
Split into simpler sentences: The project was to be the foundation of "A Comprehensive Grammar of the English Language", a widely used reference grammar. This was the first grammar of English in real use rather than one based on rules handed down from Greek and Latin models.