What are and how to use the "island grammar" in antlr3?
An island grammar is one that treats most of a language as a blob of text ("water") and picks out the part of the langauge of interest to parse using grammar rules ("island"). For instance, you might choose to build an island grammar to pick out all the expressions found in a C# program, and ignore the variable/method/class declarations and the statement syntax (if, while, ...).
The real question is, "Should you use island grammars at all?".
The positive benefits:
Call me biased, but I've been doing this kind of stuff a long time. I believe that island grammars really aren't that useful. The alternative I propose is amortized-cost parsers over many languages based on common foundations, and its called DMS Software Reengineering Toolkit.
Well I'm not sure exactly what you mean but since you haven't mentioned what you've written so far I'd start here: