Separate

It's an alternative expression for "which separate". So (looking it up) it's a reduced adverbial clause. I would have made "limits" singular, as it says there is only one fence.

So does this also work?

Separating the private world of the family from the public world beyond, the garden fence, a conspicuously displayed boundary line, often no more than a token barrier, is the outer territorial limits.

It doesn't look like a clause to me, not even a reduced one. It's a participle phrase. If I had to label it more specifically, I would say adverbial.

Aspara GusIt doesn't look like a clause to me, not even a reduced one. It's a participle phrase. If I had to label it more specifically, I would say adverbial.

So you don't think it's a modifier of 'limits', AG?

"Separating the private world of the family from the public world beyond, the garden fence, a conspicuously displayed boundary line, often no more than a token barrier, is the outer territorial limits."
It's far too long for a sentence with so many concepts joined together.This is what I think of as speed bump writing. It holds up your reading, because you have to untangle it in

TakaSo you don't think it's a modifier of 'limits', AG?

I'm not sure. Which word or phrase it modifies depends on its position in the sentence, I would think.

Separating the private world of the family from the public world beyond, the garden fence, a conspicuously displayed boundary line, often no more than a token barrier, is the outer