I was wondering why the apostrophe is not automatically escaped as other characters?

For example:

< is transformed to &lt;

and

> is transformed to &gt;

but ' is not transformed to &apos;


Python              : sys.version_info(major=2, minor=7, micro=6, releaselevel='final', serial=0)

lxml.etree          : (3, 3, 3, 0)
libxml used         : (2, 9, 1)
libxml compiled     : (2, 9, 1)
libxslt used        : (1, 1, 28)
libxslt compiled    : (1, 1, 28)