And as I wrote in the first note, accepting non-letters (that is, other than the basic unaccented Aa–Zz) makes delimited parameter patterns difficult to use with Mark VI parameter names. Thus, we have the situation described in the following example, when in fact all should work without error (as I understand it, but perhaps \starttexdefinition has other limits of which I am not aware).

% macros=mkvi

% Fails to compile with TL2013 and current beta
%\starttexdefinition Test #1¦#2.
%  #1, #2!
%\stopdefinition

% Fails to compile with TL2013 and current beta
%\starttexdefinition Test #PARAM¦#ETER.
%  #PARAM, #ETER!
%\stopdefinition