Complex Tempo Marking

[Zone Dremik]

Hello,

Does anyone have code I could use to indicate a tempo marking that shows two 
barred eighth-notes equal to a dotted eighth-note triplet?

Also, as a general inquiry, what would be needed to have notation in a markup? 
(Would this be a major Scheme coding project!?)

I've searched through the documentation, and the group postings, but I suspect 
I'm not using the right search terms. Any direction would be appreciated.

Thanks,

Zon D.