Tool to unroll nested parameter expansions

[Felix Rosencrantz <f.rosencrantz@xxxxxxxxx>]

Anyone have a tool that can take a nested parameter expression (e.g. 
pats="${(@)${(@M)tmp1:#-g*}#-g}" ) , and break it down into simpler
substeps, so it is easier to read.

Some of the completion code uses complex parameter expansions, that
are difficult to read, and it would be useful if there was something
that could break it down into smaller more understandable steps, like
a line per ${} section.

-FR.