John was causing obstruction: the act of preventing passage or progress.
The doctor said: "you need medical attention".
What do the constituents of these phrases look like?
Given that the clause after the colon is elaborating on the head noun 'obstruction', does this mean that the entire sentence is a noun phrase? or is it the case that there are two separate noun phrases, one before ':' and one after?
If not, are there any circumstances where ':' forms a noun phrase?
Does the same reasoning apply to semicolons (';')?