Silencing "Documentation issue" warnings in Xcode?

This solved it for me, surpassing the warnings only in the third party library headers. Just wrap the problematic header #includes with these pragmas:

#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wdocumentation"
#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
#pragma clang diagnostic pop

this is a combination of a hint from Konchog and Vladimir Grigorov’s super helpful answer here.

I was able to suppress these warnings by going to

Project -> Build Settings -> Apple LLVM 8.1 - Warnings - All Languages, and switching the "Documentation Comments" to No.

(To find the setting, I typed "Documentation" into the search box under Build Settings.)