nonrestrictive

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 2008

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 2010

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 2009

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."

Style in Fiction 2009

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."

October 2009 2009

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 2010

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 2009

A nonrestrictive clause is something that can be left off without changing the meaning of the sentence.

Grammar Girl: Which Versus That « Write Anything 2008

You can think of a nonrestrictive clause as simply additional information.

Grammar Girl: Which Versus That « Write Anything 2008

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 Tom Jackman 2010