Pull requests are welcome, but often it will be fruitful to first discuss it on the mailing-list.
Generally, making all the tests pass is needed for a pull request to be accepted, although sometimes a pull request can be in the form of a failing test (as a bug report). Note that NGLess has a strong culture of strict backwards compatibility, so changing behaviour requires (at the very least) discussion.
For all but the smallest changes, please list them on the ChangeLog and the
docs/source/whatsnew.rst files.