<p >The standards and mechanics w/r/t error reporting are entirely inherited from Flow. Therefore, see the <code>namespace flow</code> doc header's "Error reporting" section. It applies verbatim (within reason) here. To summarize for your convenience, though: The error reporting is based on <a class="el" href="namespaceboost_1_1system.html" title="Small group of miscellaneous utilities to ease work with boost.system, joining its boost::system name...">boost.system</a> semantics which themselves are now adop