This is not semver. This is a translucent version number. The package version does not have to follow semver semantics; it is simply sorted as semver.
Usually these three digits have this meaning:
, , . , esprima-fb : 1001.1001.2000-dev-harmony-fb. , , , semver.
edit. twitter, - .
- revisions = b/c breaks
- minors = b/c breaks
- majors = b/c
... b/c