Ensure XHTML types have the appropriate xmlns tags

[dcarbone]

Missing xmlns:

Example 1:

<!-- source -->
<div xmlns="http://www.w3.org/1999/xhtml">[Put rendering here]</div>

<!-- php-fhir -->
<div>[Put rendering here]</div>

Example 2:

<!-- source -->
<div xmlns="http://www.w3.org/1999/xhtml"/>\n

<!-- php-fhir -->
<div xmlns="http://www.w3.org/1999/xhtml" xmlns:default="http://www.w3.org/1999/xhtml"/>\n