Permute returns a Transformation that permutes the order of the stack.

Transform returns a function that generates a general-purpose Transformation.

A Transformation transforms the stack by modifying its order, growing, and/or shrinking it.

ExpectDepth is a sentinel value that singals to Code.Compile() that it must assert the expected stack depth, returning an error if incorrect.

SetDepth is a sentinel value that signals to specops.Code.Compile() that it must modify its internal counter reflecting the current stack depth.