  Branching is a feature of distributed version control systems that
facilitates the ``divide and conquer'' strategy present in complex and
collaborative work domains. Branching has revolutionized modern software
development and has the potential to similarly transform hardware product
development via CAD (computer-aided design). Yet, contrasting with its status
in software, branching as a feature of commercial CAD systems is in its
infancy, and little research exists to investigate its use in the digital
design and development of physical products. To address this knowledge gap, in
this paper, we mine and analyze 719 user-generated posts from online CAD forums
to qualitatively study designers' intentions for and preliminary use of
branching in CAD. Our work contributes a taxonomy of CAD branching use cases,
an identification of deficiencies of existing branching capabilities in CAD,
and a discussion of the untapped potential of CAD branching to support a new
paradigm of collaborative mechanical design. The insights gained from this
study may help CAD tool developers address design shortcomings in CAD branching
tools and assist CAD practitioners by raising their awareness of CAD branching
to improve design efficiency and collaborative workflows in hardware
development teams.
