leafArgumentCount

The number of underscores/ellipses present in the method name. This is not the same as the number of arguments that a method implementing this name would accept, as a top-level guillemet group with N recursively embedded underscores/ellipses is counted as N, not one.

This count of underscores/ellipses is essential for expressing negative precedence rules (grammatical restrictions) in the presence of repeated arguments. Also note that backquoted underscores are not counted, since they don't represent a position at which a subexpression must occur. Similarly, backquoted ellipses are not a place where an arbitrary input token can go.