RFC4466 (2006): Collected Extensions to IMAP4 ABNF

Supporting RFC4466 as well as the basic ABNF in RFC3501 will give significant forward compatibility, allowing us to partially parse some other extensions which we don't (yet?) otherwise support. Additionally, RFC4466 support is necessary for RFC9051.

• Parse unknown or unsupported extensions using RFC4466 tagged-ext syntax
  • Parse tagged-ext-val (done as part of #225)
  • Add ExtensionData (done as part of #225)
  • #127
  • #128
  • #129
    (also usable for non-RFC4466 extension data)
• RFC4466 2.1: Optional Parameters with the #select/#examine Commands
  • #124
  • Add kwargs to #select/#examine for existing select-param extensions
    • #122
    • #123
• RFC4466 2.2: Extended #create Command
  • #126
  • Add kwargs to #create for existing create-param extensions
    • #125
• RFC4466 2.3: Extended #rename Command
  • #130
• RFC4466 2.4: Extensions to #fetch and #uid_fetch Commands
  • #133
  • Add kwargs to #fetch/#uid_fetch for existing fetch-modifier extensions
    • #132
    • #131
• RFC4422 2.6: Extensions to #search Command
  • #115
    • Add arbitrary return opts to #search, using search-return-opts syntax (RFC4466 tagged-ext)
  • #121
    • #120
    • Parse all existing search-return-data extensions directly
• RFC4422 2.7: Extensions to #append Command
  • #535
  • #537
  • #536

Start by reviewing RFC4466, RFC3501, and RFC9051, then inspect the outstanding linked issues (#123, #124–#131, #133, and #536–#537) to identify the remaining implementation scope. Done means the unchecked RFC4466 parsing and command-extension items in this checklist are implemented and covered by the relevant project tests.