[antlr-interest] A very basic grammar--and I'm confused!

[Richard Steele]

I'm missing something really basic here and would appreciate some help.  I'm not
new to the subject--but it has been a few years and I must have forgotten
everything I (thought?) I knew.

I have a really simple grammar:

grammar R;

r	:	'X' ID;
ID	:	'A'..'Z'+;

However, this returns a MismatchedTokenException for every (alphabetic) input. 
It appears that the 'X' is getting greedily swallowed by the expression for ID,
but I don't understand why that would be, nor how to prevent it from happening.
 (If I change the 'X' to '1', or anything else not in ID, then it works as I
expect.)

Can anyone (gently) help?

Thanks,
Rich