There is no corresponding research on Estonian parentheticals and most probably there would be crucial differences between the two languages, especially in regard to pitch movement.
When it comes to the semantic development of first person epistemic parentheticals, Traugott (1995) notes that the subject may lose referential (objective) properties, and become simply the starting point of a perspective.
22) When a string of citations is used, it is more persuasive with proper use of introductory signals and explanatory parentheticals
that explain the relevance of each citation.
There is no reason to insert parentheticals
systematically after any authority introduced by the signal see.
Wherever possible, citations should be handled as in-text parenthetical
citations, especially when the source of a quote or a paraphrase has already been mentioned in the text, and when there is no possibility for confusion.
Secondly, in Brinton's analysis of I gesse, I trowe, and the like, she presents a fascinating thesis that these parentheticals
serve entirely different functions in the narratological report and in characters' dialogue.
The frequent occurrence of parentheticals
is almost equally strong evidence.
Citations to cases are listed by circuit and include detailed parentheticals
A citation consists of three basic parts: an introductory signal stating the nature of the support provided, a description of the authority, and an optional parenthetical
phrase explaining its relevance to the subject matter.