Hg: How to mark a changeset as 'stable'

As the repository of hg itself, some changesets 开发者_Python百科are marked with 'stable'. I am wondering how to add the 'stable' mark to changesets. I had googled but it doesn't help. I tried 'hg help tag' but still can not figure out how to do it. Do I miss something very basic?

Thanks in advance.

I believe they are not "marked" as stable.

Those commits are part of the branch 'stable' history.

See the graph:

This is named branch, not tag. hg help branch, or better read Mercurial Book: http://hgbook.red-bean.com/read/managing-releases-and-branchy-development.html