While the Domino Designer help files describe the @command([OpenCalendar];Username) as a very simple command that will open a users calendar there is an extra undocumented parameter that will instruct the notes client to open the users calendar in the proper calendar frameset.
@command([OpenCalendar];username;[UseFrameSet]) will open the calendar in the calendar frameset.
@command([OpenCalendar];username;[UseMailFrameSet]) will open the users inbox in the mail frameset.
So why is this undocumented? The ND6 mail template uses the undocumented commands as part of it’s functionality to open listed users calendars. Infact why keep things that are useful hidden in the product. Every version of the Notes client that has come out has always had something hidden, like the formula debugger in R5 and the extra admin panel options in R4.
What else is hidden in there that we don’t know about?
Dec's Dom Blog 
Well, not to defend the Lotus developers too strongly, but the examples explain the problem. What if they had documented the formula debugger? Now, they would be obligated to support it, and instead they have been able to scrap it.
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There are two main reasons why programmatic features aren’t documented:
1) they were added specifically for a particular template, in an exact use scenario, and the use of the new feature hasn’t been fully QAed or tested for general use;
2) it was tested, but just didn’t make it into the docs in time – therefore it is “undocumented” (@ReplaceSubstring and @URLEncode are prime examples of this from prior releases).
And there are features they were trying out, but couldn’t get ready for primetime – such as the aforementioned formula debugger. It was never officially announced because it blew up on forms containing RT fields. Same goes for Difference of Two Docs – it blew up on RT fields as well.
Damned RT fields (That’s for you, Ben )
Rock
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Does that command work in R5?
I tried it and it choked on the ‘UseFrameSet’ reference…
Thx.
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