How To Use Nonrestrictive In A Sentence

You use which in nonrestrictive clauses, and if you eliminate a nonrestrictive clause, the meaning of the remaining part of the sentence will be the same as it was before. Grammar Girl: Which Versus That « Write Anything
You can think of a nonrestrictive clause as simply additional information. Grammar Girl: Which Versus That « Write Anything
the nonrestrictive clause in `I always buy his books, which have influenced me greatly,' refers to his books generally and adds an additional fact about them
At the same time, the instruction to put a comma before a nonrestrictive clause is not unique to Strunk & White but can be found in many writing texts. The Volokh Conspiracy » From Language Log to the New York Times Magazine
A nonrestrictive clause is something that can be left off without changing the meaning of the sentence. Grammar Girl: Which Versus That « Write Anything

The first three lines encourage us to read without pausing but the forced pause created by the quotation marks around "genial" allow us to catch our breath before moving on through the next two lines and arriving at the inserted nonrestrictive "in my youth. Kerouac the Writer
Heffner argued that there was too big a gap between PG and R and the studios were constantly trying to get more and more “adult material” into the “nonrestrictive” lower rating because it meant greater profit potential for them, and Heffner correctly foresaw that someday this would come back to bite them. Current Movie Reviews, Independent Movies - Film Threat
If it were about any subject other than the “On Language” column, the press release would be unremarkable for failing to use a comma in its second sentence before the nonrestrictive relative clause “who was the founding and regular columnist until his death last fall.” The Volokh Conspiracy » From Language Log to the New York Times Magazine
Reid noted that the phrase "when approaching from any direction" is a nonrestrictive modifier and can be removed from the sentence. Dropped 'at' in Va. law yields acquittal in school bus case