Part: Add comment explaining element map version string

src/Mod/Part/App/TopoShapeExpansion.cpp

@@ -2063,6 +2063,9 @@ static const std::string& _getElementMapVersion()
     if (_ver.empty()) {
         std::ostringstream ss;
         unsigned occ_ver;
+        // Stabilize the reported OCCT version: for any version of OpenCASCADE in the 7.x series,
+        // report 7.2.0 as the version so that we aren't constantly inadvertently reporting differing
+        // versions. This is retained for cross-compatibility with LinkStage3.
         if ((OCC_VERSION_HEX & 0xFF0000) == 0x070000) {
             occ_ver = 0x070200;
         }