1. Introduction

RFC 2119 specifies common key words, such as "MUST", "SHOULD", and "MAY", that may be used in protocol specifications. It says that the key words "are often capitalized," which has caused confusion about how to interpret non-capitalized words such as "must" and "should".

This document updates RFC 2119 by clarifying that only UPPERCASE usage of the key words have the defined special meanings. This document is part of BCP 14.

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