[OT] Markaby How to yield to a capture block?

Please excuse me if this is not the right forum. I looked for a markaby one
but couldn't find one. I'd like to be able to yield a builder type object,
or any args really, to a capture block in markaby.

Something like this

capture( MyBuilder.new ) do |builder|
  p builder.some_text_returning_method

How can I do this?