Attribute accessors

I was fixing up my code for the recent change to the attribute macros that removed the class type and changed the variant type from the VAR_* to the actual type and I am wondering since there are no comments for these. Could comments be added on the macros in Serializable.h at the bottom to define what their uses are? My IDE expands the macros to show me what the final code is like when I hover over, but there is no comment to define the use since there is no comment on the line prior to each macro.

Also, the new Mixed attribute accessor is useful, thanks!