Say you have a rotation matrix $R$ and a translation matrix $t$, you can trivially have a single matrix $[\;R\;|\;t\;]$. Now say you have another matrix $R'$, can you write $R'[\;R\;|\;t\;]$ as $[\;R''\;|\;t'\;]$? I would think yes, but I would like to be sure.
Edit: $[\;R\;|\;t\;]$ is a rotation matrix with the right most colomn a translation. It's the same as applying the rotation $R$ first followed by the translation $t$. This might indeed be somewhat of a funky notation but it is used in the following book: http://szeliski.org/Book/. For example on page 50.