Recently on the Copyediting-L discussion board, member Levi Bookin presented this conundrum: one of his authors avoids the phrase such as to such an extreme that he seems allergic to it. Possibly, Bookin wrote, this is because he dislikes commas so much. For example:
Such parties as the XYZ Alliance lost their members and supporters.
Bookin worried that something was amiss with the sentence, however. In splitting the such as phrase, the author avoided "Parties such as the XYZ Alliance lost their members and supporters," perhaps really trying to avoid "Parties, such as the XYZ Alliance, lost their members and supporters." Did the meaning change when "such parties as the XYZ Alliance" was used instead of "parties such as the XYZ Alliance"?
List members tossed around various thoughts and explanations. Was the example party essential to the sentence? In other words, was the XYZ Alliance a restrictive example?
Throughout the conversation, the humble comma that the author dislikes so much was barely mentioned, perhaps because Bookin was trying to avoid it in his edit.
The problem, though, is that the comma, and by extension its absence, affected the meaning.
Restrictive vs. Nonrestrictive
One use of commas is to set off parenthetical, or extra, information (as they do in this sentence). The extra information isn't necessary to the meaning of the sentence. Take the commas out, and the meaning remains the same:
Tommy walks his dog, a Siberian Husky, every day.
Tommy walks his dog every day.
While the second example doesn't tell us what type of dog Tommy owns, the absence of that information doesn't change the fact that Tommy walks the dog each day.
Sometimes, though, deciding when the information is necessary or not, that is, whether it is restrictive or nonrestrictive, is more difficult. You were probably taught about restrictive and nonrestrictive in terms of that and which. A restrictive phrase limits the original idea it refers to, while a nonrestrictive phrase simply adds more information about the original idea:
I picked up the books that were on the table.
Usually my mail, which is delivered at noon, is nothing but bills.
In the first example, I mean a specific subset of books: the ones on the table, not the ones somewhere else. I've specified which books I'm talking about. In the second example, the time my mail is delivered doesn't affect what the mail is; it's just extra information.
Although Americans pair which with a comma and leave the comma off with that, it's really the comma that tells the reader whether the item in question is restrictive or nonrestrictive, just as it does in similar structures:
Joan pointed out the boy who told her a lie.
Joan pointed out the boy, who told her a lie.
Joan identifies the specific boy who lied to her in the first sentence, while in the second sentence Joan just identifies the boy. The fact that told her a lie doesn't distinguish him from the group he's in. Maybe he's the only boy in the group. Maybe the boy lied after Joan pointed him out. We can't say for sure because the sentence doesn't tell us.
And that's what is happening with our such as example. Without the commas, the such as phrase is restrictive. The type of parties being talked about are only the ones that lost members and supporters, not those parties that gained members and supporters or whose members and supports didn't change. The XYZ Alliance is among those parties that grew smaller. To say "such parties as the XYZ Alliance" is to make that same restriction.
If the author means to point to a subset of parties — those that lost members and supporters — then there's nothing wrong with "Such parties as the XYZ Alliance lost their members and supporters."