If a particular portion of the FreeBSD src/ distribution is being maintained by a person or group of persons, this is communicated through an entry in the src/MAINTAINERS file. Maintainers of ports within the Ports Collection express their maintainership to the world by adding a MAINTAINER line to the Makefile of the port in question:
MAINTAINER= email-addresses
Tip: For other parts of the repository, or for sections not listed as having a maintainer, or when you are unsure who the active maintainer is, try looking at the recent commit history of the relevant parts of the source tree. It is quite often the case that a maintainer is not explicitly named, but the people who are actively working in a part of the source tree for, say, the last couple of years are interested in reviewing changes. Even if this is not specifically mentioned in the documentation or the source itself, asking for a review as a form of courtesy is a very reasonable thing to do.
The role of the maintainer is as follows:
The maintainer owns and is responsible for that code. This means that he or she is responsible for fixing bugs and answering problem reports pertaining to that piece of the code, and in the case of contributed software, for tracking new versions, as appropriate.
Changes to directories which have a maintainer defined shall be sent to the maintainer for review before being committed. Only if the maintainer does not respond for an unacceptable period of time, to several emails, will it be acceptable to commit changes without review by the maintainer. However, it is suggested that you try to have the changes reviewed by someone else if at all possible.
It is of course not acceptable to add a person or group as maintainer unless they agree to assume this duty. On the other hand it does not have to be a committer and it can easily be a group of people.