RFC 2447, 3339, 4791, 4918, 5545, 5546, 5988 are a "proposed standard". This is the lowest level of "internet standard" requiring a minimum of 6 months at this state, followed by a minimum of 4 months at "draft standard" state, before being considered an "internet standard". There is always danger is referencing and/or relying upon draft documents that may ultimately change and force a change in the referencing standard. perhaps WS-Calendar should not have "normative" references that are not full standards.