Example Semantics
float4 myColor : DIFFUSE;
float4x4 myMat : WORLDVIEW;
float elapsed : TIME;
Screenshot of page from the FX Composer help.  This page is generated from fxmapping.xml, which tells FX Composer how to map semantics/annotations to it’s internal values, and has validation information for types in fxmapping.
Example semantics – DIFFUSE and WORLDVIEW, conformant with the spec.