When can we use a colon after a dash?

Question

This is from The Development of Human Rights Law by the Judges of the International Court of Justice by Shiv R.S. Bedi:

If, as Prof Brownlie states—:'Sovereignty, or sovereignty and independence, are often the terms used to describe both the legal personality of a state and teh incidents of that personality'—then what would be the effect on sovereignty, or in other words how much would it be conditioned by, of the principle of human dignity which, by already conditioning the State sovereignty in the first instance, has given birth to a new 'legal personality', the individual human being, in the international law?

Can someone tell me when we can use a colon after a dash? I've honestly never seen it and never seen such combination mentioned in a style book.

Answer 1

It is not well punctuated. Although house styles will vary, the colon is used to introduce a quote after a complete sentence:

Prof. Brownlie has much to say on the relationship between the individual and the state: "Sovereignty, or ..."

In this example, the quote is incorporated into the sentence and so should receive only the same punctuation that it would have had if it was not a quote. A comma is required for the parenthetical phrase "as Prof. Bronwnlie states". No other punctuation is required:

If, as Prof Brownlie states, 'sovereignty, or sovereignty and...'

It is not ungrammatical to use "—:" but it is odd and not needed.