[ns3:~/linkrabbit] administrator% brew install libxml2
<snip>
==> Downloading https://homebrew.bintray.com/bottles/libxml2-2.9.7.sierra.bottle.tar.gz
######################################################################## 100.0%
==> Pouring libxml2-2.9.7.sierra.bottle.tar.gz
==> Caveats
This formula is keg-only, which means it was not symlinked into /usr/local,
because macOS already provides this software and installing another version in
parallel can cause all kinds of trouble.

If you need to have this software first in your PATH run:
  echo 'export PATH="/usr/local/opt/libxml2/bin:$PATH"' >> ~/.bash_profile

For compilers to find this software you may need to set:
    LDFLAGS:  -L/usr/local/opt/libxml2/lib
    CPPFLAGS: -I/usr/local/opt/libxml2/include
For pkg-config to find this software you may need to set:
    PKG_CONFIG_PATH: /usr/local/opt/libxml2/lib/pkgconfig


If you need Python to find bindings for this keg-only formula, run:
  echo /usr/local/opt/libxml2/lib/python2.7/site-packages >> /usr/local/lib/python2.7/site-packages/libxml2.pth
  mkdir -p /Users/administrator/Library/Python/2.7/lib/python/site-packages
  echo 'import site; site.addsitedir("/usr/local/lib/python2.7/site-packages")' >> /Users/administrator/Library/Python/2.7/lib/python/site-packages/homebrew.pth
==> Summary
&#127866;  /usr/local/Cellar/libxml2/2.9.7: 281 files, 10.4MB

[ns3:~/linkrabbit] administrator% echo 'export PATH="/usr/local/opt/libxml2/bin:$PATH"' >> ~/.bash_profile

<logout/login>

[ns3:~] administrator% cd ~/src/XML-LibXML-2.0132
[ns3:~/src/XML-LibXML-2.0132] administrator% perl Makefile.PL -I/usr/local/opt/libxml2/include 
enable native perl UTF8
running xml2-config...failed
The installed version of libxml2 VERSION 2.9.4
 is not compatible with XML::LibXML (and probably buggy)!