[antlr-interest] Viable Alternative Rule?

[Ted Hoise]

VERY simple example

rule : 'H'  ;

When I test this very simple rule, it works (in Antlrworks and Eclipse) of course for input 'H', but it also works for input 'fH', resulting in a token 'fH'.  I do I suppress this behavior:  it seems like an error should occur.