To specify the branch to use for resolving the next keyref in a map or a topic, insert a KeyrefBranch PI:
<?dtall keyrefbranch="BranchName" ?>
A KeyrefBranch PI specifies the name of the branch to search to resolve the next keyref only, either in a map or in a topic. It works the same way as cross-reference branch PIs and conref branch PIs; see:
§9.6.4 Directing a cross reference to the correct branch
§9.6.5 Directing a content reference to the correct branch
Using the example in §9.6.6 Limiting the scope of keydefs by branch, if a topic contains:
<?dtall keyrefbranch="Revisited" ?><term keyref="OS"/>
the term becomes “Linux” even if the keyref is in the Windows chapter.