How to set NSConstraintBasedLayoutVisualizeMutuallyExclusiveConstraints?

You can configure the setting for a particular scheme as follows ...

1) Select the scheme from the popup menu and choose Edit Scheme ...

2) In the following slide down window add a new entry to Arguments Passed on Launch.
Copy and paste the following line.

-NSConstraintBasedLayoutVisualizeMutuallyExclusiveConstraints YES

You may also set

Objective C:

[[NSUserDefaults standardUserDefaults] setBool:YES forKey:@"NSConstraintBasedLayoutVisualizeMutuallyExclusiveConstraints"];

Swift <3:

NSUserDefaults.standardUserDefaults().setBool(true, forKey: "NSConstraintBasedLayoutVisualizeMutuallyExclusiveConstraints")

Swift 3-4.2 (at least):

UserDefaults.standard.set(true, forKey: "NSConstraintBasedLayoutVisualizeMutuallyExclusiveConstraints")

in applicationDidFinishLaunching.

Note that this will set it for both yourself and your end-users, which may not be what you want (don't go into production like this!). You can set it only for yourself by setting the -NSConstraintBasedLayoutVisualizeMutuallyExclusiveConstraints YES argument in your "Debug" run scheme (described in a separate answer).