[antlr-interest] Q: How to understand 'multiple alternatives'?

[Austin Hastings]

Howy,

I'm parsing a C-like language, and I'm getting this kind of warning:

warning(200): perl6/hlasm/Hlasm.g3:245:4: Decision can match input such 
as "'&'" using multiple alternatives: 1, 2
As a result, alternative(s) 2 were disabled for that input

In several places. In fact, the '&' (and several other characters) can 
have different roles to play in the language. In this case, & can either 
be a bitwise and, or an address operator.

However -- and this is what confuses me -- I can't seem to see what 
antlr is griping about. According to me, and expression like

a & b

should not be confusable with

&foo

so I'm wondering why antlr seems to feel that there are different 
alternatives that can parse the &.

Obviously, either there's a problem with antlr or a problem with my 
grammar. I'd like it to be with my grammar, since I can likely fix that.

So my question is, how do I understand what the multiple alternatives 
are, here? I tried dumping the nfa/dfas, to little avail.

Recommendations, advice?

=Austin