The requirement for at least two independent and interoperable implementations applies to all of the options and features of the
specification.  In cases in which one or more options or features have not been demonstrated in at least two interoperable
implementations, the specification may advance to the Draft Standard level only if those options or features are removed.

The Working Group chair is responsible for documenting the specific implementations which qualify the specification for Draft or Internet Standard status along with documentation about testing of the interoperation of these implementations.  The documentation must include information about the support of each of the individual options and features.  This documentation should be submitted to the Area Director with the protocol action request. (see Section 6)

A Draft Standard must be well-understood and known to be quite stable, both in its semantics and as a basis for developing an
implementation.  A Draft Standard may still require additional or more widespread field experience, since it is possible for
implementations based on Draft Standard specifications to demonstrate unforeseen behavior when subjected to large-scale use in production environments. A Draft Standard is normally considered to be a final specification, and changes are likely to be made only to solve specific problems encountered.  In most circumstances, it is reasonable for vendors to  deploy implementations of Draft Standards into a disruption sensitive environment.

1. MUST   This word, or the terms "REQUIRED" or "SHALL", mean that the definition is an absolute requirement of the specification.
2. MUST NOT   This phrase, or the phrase "SHALL NOT", mean that the definition is an absolute prohibition of the specification.
3. SHOULD   This word, or the adjective "RECOMMENDED", mean that there may exist valid reasons in particular circumstances to ignore a particular item, but the full implications must be understood and carefully weighed before choosing a different course.
4. SHOULD NOT   This phrase, or the phrase "NOT RECOMMENDED" mean that there may exist valid reasons in particular circumstances when the particular behavior is acceptable or even useful, but the full implications should be understood and the case carefully weighed before implementing any behavior described with this label.
5. MAY   This word, or the adjective "OPTIONAL", mean that an item is truly optional.  One vendor may choose to include the item because a particular marketplace requires it or because the vendor feels that it enhances the product while another vendor may omit the same item. An implementation which does not include a 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 a 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.)

RFC 2445 - Condition Matrix
RFC 2446 (iTIP) - Condition Matrix
RFC 2447 (iMIP) - Condition Matrix