  A study is presented of anomalous HVV interactions of the Higgs boson,
including its $CP$ properties. The study uses Higgs boson candidates produced
mainly in vector boson fusion and gluon fusion that subsequently decay to a
pair of $\tau$ leptons. The data were recorded by the CMS experiment at the LHC
in 2016 at a center-of-mass energy of 13 TeV and correspond to an integrated
luminosity of 35.9 fb$^{-1}$. A matrix element technique is employed for the
analysis of anomalous interactions. The results are combined with those from
the H $\to 4\ell$ decay channel presented earlier, yielding the most stringent
constraints on anomalous Higgs boson couplings to electroweak vector bosons
expressed as effective cross section fractions and phases: the $CP$-violating
parameter $f_{a3}\cos(\phi_{a3})$ $=$ $(0.00 \pm 0.27) \times 10^{-3}$ and the
$CP$-conserving parameters $f_{a2}\cos(\phi_{a2})$ $=$ $(0.08 ^{+1.04}_{-0.21})
\times 10^{-3}$, $f_{\Lambda1}\cos(\phi_{\Lambda1})$ $=$ $(0.00
^{+0.53}_{-0.09}) \times 10^{-3}$, and
$f_{\Lambda1}^{\mathrm{Z}\gamma}\cos(\phi_{\Lambda1}^{\mathrm{Z}\gamma})$ $=$
$(0.0 ^{+1.1}_{-1.3}) \times 10^{-3}$. The current dataset does not allow for
precise constraints on $CP$ properties in the gluon fusion process. The results
are consistent with standard model expectations.
