Some VCS reports revisions number from which it is possible to deduce the related branches. This is the case in CVS for example where a revision number for a branch uses as prefix the branch point revision number. For such VCS it is possible to specify two regular expressions:
parent_revision
<parent_revision regexp="..." />
For CVS on 1.2.4.5 it must match 1.2.
branch_root_revision
<branch_root_revision regexp="..." />
For CVS on 1.2.4.5 it must match 1.2.4.