This article is about rhetoric and syntax, not about a punctuation.
In rhetoric a parenthesis or parenthetical clause is an explanatory phrase or just one word inserted into the sentence. Such phrase may be omitted without loosing a sense of passage, however parentheses may better describe it or express attitude of the speaker or writer to events or person. Parenthesis often treated as modifier phrases but often do not carry any syntactical role at all. They are often expressed by adverbials, conjunctions and impersonal clauses.
Typical applications of parenthesis include:
Any longer dependent clause describing the person or action of main sentence may be used similarly as parenthesis. Many modifier and adverbial dependent clauses inserted in the middle of the sentence belong to this category. For example:
Of course, such long sentences as the last two belong to fiction literature and do not occur in normal conversation, being not very suitable for Orcs' speech.
Such phrases should be separated by punctuation marks in written speech. But Tengwar and Cirth are limited with them. It's suggested to use “two vertical dots” (means comma but look like colon) in Cirth.