supplementive clauses need not be separated from their matrix clause intonationally when they occur in final position

[diamondcutter]

In spite of their resemblance to nonrestrictive relative clauses, supplementive clauses need not be separated from their matrix clause intonationally when they occur in final position. The following are therefore alternative renderings of the same sentence, differing only in that [1] has two focuses of information, whereas [2] has only one:
The manager APPROACHED us, SMILING. [1]
The manager approached us SMILING. [2]
Source: A Comprehensive Grammar of the English Language by Randolph Quirk, Sidney Greenbaum, Geoffrey Leech.

I don’t quite understand this sentence: supplementive clauses need not be separated from their matrix clause intonationally when they occur in final position. Does it mean that taking the sample sentences as an example, it’s not necessary to put a comma before the participle “smiling” and if you put, there will be two focuses of information: approached and smiling?

 

[jutfrank]

Yes, that's right. In writing, the comma represents the intonation one would use to separate the sentence into two focuses of information.