  This is the second in a series of "graphical grokking" papers in which we
study how stabiliser codes can be understood using the ZX calculus. In this
paper we show that certain complex rules involving ZX diagrams, called spider
nest identities, can be captured succinctly using the scalable ZX calculus, and
all such identities can be proved inductively from a single new rule using the
Clifford ZX calculus. This can be combined with the ZX picture of CSS codes,
developed in the first "grokking" paper, to give a simple characterisation of
the set of all transversal diagonal gates at the third level of the Clifford
hierarchy implementable in an arbitrary CSS code.
