&gt; The extension mechanism is open, allowing programs using Transit to add new elements specific to their needs. Users of data formats without such facilities must rely on either schemas, convention, or context to convey elements not included in the base set,<p>The extension mechanism is writing handlers in all languages communicated with, since its stated purpose is cross language value conveyance.<p>In contrast, a schema language allows extensions to be described once, in one language.<p>I was expecting this to be a sort of macros for data notation (an inline schema language), but it seems more like an extendible serialization library.