lpeg.Carg() weirdness

[Sean Conner <sean@...>]

  I have an issue where I thought using lpeg.Carg() would solve the issue. 
As a test, I wrote:

	lpeg = require "lpeg"
	pat  = lpeg.P"a" * lpeg.Carg(1)

	x = pat:match(pat)
	print(x)

And I get:

	lua: y.lua:4: reference to absent extra argument #1
	stack traceback:
	        [C]: in function 'match'
	        y.lua:4: in main chunk
	        [C]: ?

Yet if I do:

	x = pat:match(pat,1,nil)
	print(x)

	nil

  So, what, exactly *is* the difference between the two calls?  I mean,
besides the explicit nil being given in the second call.

  -spc (Bummed about this ... )