[boost] Sandbox and externals

Hi, could someone please tell me whether the use of SVN externals is allowed in the Boost Sandbox? For example, I'm working on two projects/libraries and have a header that is a collection of various platform specifics that I'd like to use in both libraries but would also like to not have to manually update two copies of it (rather have one of the libraries use it as a SVN external)... I was unable to find this information at https://svn.boost.org/trac/boost/wiki/BoostSandbox... -- "What Huxley teaches is that in the age of advanced technology, spiritual devastation is more likely to come from an enemy with a smiling face than from one whose countenance exudes suspicion and hate." Neil Postman