This option controls whether or not nonstandard template argument deduction is to be performed in the qualifier portion of a qualified name in C++.
With this feature enabled, a template argument for the template
T can be deduced in contexts like
The standard deduction mechanism treats these as nondeduced contexts
that use the values of template parameters that were either explicitly
specified or deduced elsewhere.
provided only as a migration aid for legacy source code that does
not conform to the C++ standard. Its use is not recommended.