!!! Overview
[{$pagename}] or the terms "[REQUIRED]" or "[MUST]" ([RFC 2119]), which are [Case-sensitive] ([RFC 8174]), mean that the definition is an absolute requirement of the specification.

An implementation which does not include this particular option [MUST] be prepared to interoperate with another implementation which does include the option, though perhaps with reduced functionality. 

In the same vein an implementation which does include this particular option [MUST] be prepared to interoperate with another implementation which does not include the option (except, of course, for the feature the option provides.)

We may use [{$pagename}] in other contexts but we are implying the same interpretation as a [Best Current Practice]

!! More Information
There might be more information for this subject on one of the following:
[{ReferringPagesPlugin before='*' after='\n' }]