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- Improve error messages when backtracking or using arbitrary lookahead
- Make a real interpreter using NFA; allow access as library from Java code
- Tokens and Trees should both know their start/stop line, start/stop char position to make IDEs easier.
- Tree parser error handling should skip subtrees not nodes; these are programming errors not input errors. The flat stream makes it hard to resync.
Miscellaneous
- Default rule parameter values, same for scope fields.
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