Idea under GRC

Hi, Josh,Could you distribute some documents about how to implementing
the function of generating code in GRC? How to add new graphic signal
processing block in GRC?I hope to get to know some ideas on designing
GRC, such as why do you extract five basic primitives in XML: block,
parameter, key, value, connection? Why do not choose some other
primitives?How to translate the XML present to python Language?Or anyone
have some ideas on it?Please let me know if anyone have some idea on