docs/changelogs/v0.10.md
> See [commit history](https://github.com/pegjs/pegjs/compare/v0.9.0...v0.10.0) for a full list of changes.
## v0.10.0 _(August 19, 2016)_
### Major Changes
* **Parsers can be generated in multiple module formats.**
The available formats are: CommonJS (the default), AMD, UMD, globals, and bare (not available from the command-line).
The format can be specified using the `format` option of the `peg.generate` function or the `--format` option on the command-line.
It is also possible to specify parser dependencies using the `dependencies` option of the `peg.generate` function or the `--dependency`/`-d` option on the command-line. This is mainly useful for the UMD format, where the dependencies are translated into both AMD dependencies and CommonJS `require` calls.
* **Browser version of PEG.js is now in the UMD format.**
This means it will try to detect AMD or Node.js/CommonJS module loader and define itself as a module. If no loader is found, it will export itself using a global variable.
* **API polishing.**
The `peg.buildParser` function was renamed to `peg.generate`. The global variable the browser version of PEG.js is available in when no loader is detected was renamed from `PEG` to `peg`.
* **CLI improvements.**
There is new `--output`/`-o` command-line option which allows to specify the output file. The old way of specifying the output file using a second argument was removed. To make room for the new `-o` option the old one (a shortcut for `--optimize`) was renamed to `-O`. All these changes make PEG.js conform to traditional compiler command-line interface.
It is now also possible to use `-` as a file name on the command-line (with the usual meaning of standard input/output).
* **Improved error messages.**
Both messages produced by PEG.js and generated parsers were improved.
* **Duplicate rule definitions are reported as errors.**
* **Duplicate labels are reported as errors.**
### Minor Changes
* Exposed the AST node visitor builder as `peg.compiler.visitor`. This is useful mainly for plugins which manipulate the AST.
* Exposed the function which builds messages of exceptions produced by generated parsers as `SyntaxError.buildMessage`. This is useful mainly for customizing these error messages.
* The `error` and `expected` functions now accept an optional `location` parameter. This allows to customize the location in which the resulting syntax error is reported.
* Refactored expectations reported in the `expected` property of exceptions produced by generated parsers. They are no longer de-duplicated and sorted, their format changed to be more machine-readable, and they no longer contain human-readable descriptions.
* The `found` property of exceptions produced by the `error` function is now set to `null`.
* Removed access to the parser object in parser code via the `parser` variable.
* Made handling of optional parameters consistent with ES 2015. Specifically, passing `undefined` as a parameter value is now equivalent to not passing the parameter at all.
* Renamed several compiler passes.
* Generated parsers no longer consider `\r`, `\u2028`, and `\u2029` as newlines (only `\n` and `\r\n`).
* Simplified the arithmetic's example grammar.
* Switched from `first`/`rest` to `head`/`tail` in PEG.js grammar and example grammars.
* Started using ESLint instead of JSHint and fixed various problems it found.
* Added [contribution guidelines](https://github.com/pegjs/pegjs/blob/master/CONTRIBUTING.md).
* Removed support for io.js.
### Bug Fixes
* Fixed `bin/pegjs` so that invoking it with one non-option argument which is an extension-less file doesn’t cause that file to be overwritten.
* Fixed label scoping so that labels in expressions like `(a:"a")` or `(a:"a" b:"b" c:"c")` aren’t visible from the outside.
* Fixed escaping of generated JavaScript strings & regexps to also escape DEL (U+007F).
* Fixed the JSON example grammar to correctly handle characters with code points above U+10FF in strings.
* Fixed multiple compatibility issues of `tools/impact` on OS X.
* Fixed slow deduplication of expectation descriptions.