install doc with python group

[db]

Which is the proper way to install documentation with python group?

This boilerplate works for the subport but not if I install the main port.

post-destroot {
    set docdir ${prefix}/share/${subport}
    xinstall -d ${destroot}${docdir}
    xinstall -m 644 -W ${worksrcpath} \
        CHANGES.txt \
        LICENSE \
        README.rst \
        ${destroot}${docdir}
}

Here's an extract from the log.

:debug:destroot Executing org.macports.destroot (py-setuptools_hg)
:debug:destroot system: echo py-setuptools_hg is a stub port > /opt/local/var/macports/build/_opt_local_myports_python_py-setuptools_hg/py-setuptools_hg/work/destroot/opt/local/share/doc/py-setuptools_hg/README
:debug:destroot Executing proc-post-org.macports.destroot-destroot-0
:info:destroot xinstall: mkdir /opt/local/var/macports/build/_opt_local_myports_python_py-setuptools_hg/py-setuptools_hg/work/destroot/opt/local/share/py-setuptools_hg
:error:destroot Failed to destroot py-setuptools_hg: xinstall: Unable to chdir to /opt/local/var/macports/build/_opt_local_myports_python_py-setuptools_hg/py-setuptools_hg/work/setuptools_hg-0.4, No such file or directory
:debug:destroot Error code: NONE
:debug:destroot Backtrace: xinstall: Unable to chdir to /opt/local/var/macports/build/_opt_local_myports_python_py-setuptools_hg/py-setuptools_hg/work/setuptools_hg-0.4, No such file or directory
:debug:destroot     while executing
:debug:destroot "$post $targetname"
:error:destroot See /opt/local/var/macports/logs/_opt_local_myports_python_py-setuptools_hg/py-setuptools_hg/main.log for details.