Updated ModelMeshPart (markdown)

ModelMeshPart.md

@@ -43,7 +43,7 @@ All members of ModelMeshPart are public to facilitate writing custom model loade
 
 * _vertexStride_ - Stride in bytes for each vertex in the vertex buffer associated with this submesh. This is used when calling Direct3D 12's ``IASetVertexBuffers`` method.
 
-* _vertexCount_ - Number of vertices in the vertex buffer associated with this submesh.
+* _vertexCount_ - Number of vertices in the vertex buffer associated with this submesh. *This is optional metadata and can be 0 if unknown.*
 
 * _vertexBufferSize_ - Size of the vertex buffer. This is used when calling Direct3D12's ``IASetVertexBuffers`` method.