I'm curious about the history and use of parenthetical phrases within dialog. I offer two contrasting examples:
An example of an "unvoiced" parenthetical phrase inside dialog from Pride and Prejudice (1823) chapter 18, when Sir William Lucas interrupts Elizabeth and Mr. Darcy during their dance at the Netherfield ball:
"I have been most highly gratified indeed, my dear Sir. Such very superior dancing is not often seen. It is evident that you belong to the first circles. Allow me to say, however, that your fair partner does not disgrace you, and that I must hope to have this pleasure often repeated, especially when a certain desirable event, my dear Miss Eliza (glancing at her sister and Bingley), shall take place. What congratulations will then flow in! I appeal to Mr. Darcy: -- but let me not interrupt you, Sir. -- You will not thank me for detaining you from the bewitching converse of that young lady, whose bright eyes are also upbraiding me."
And a contrasting "voiced" example from Whose Body (1923, the first Lord Peter Wimsey novel by Dorothy Sayers):
"Bosh!" said Lord Peter. "I am retained (by old Mrs. Thipps, for whom I entertain the greatest respect) to deal with this case, and it's only by courtesy I allow you to have anything to do with it."
There are many such examples in Whose Body. There are also examples in Pride and Prejudice.
In a modern novel I would expect that the unvoiced parenthetical would be rewritten to eliminate it and that the voiced parenthetical is probably replaced by text offset by emdash. But I would be interested in counterexamples.