These functions/constants are available since PHP 5.1.0 and if you have compiled one of the extensions based on libxml, like DOM, SimpleXML and XSLT.
This extension requires libxml >= 2.6.0.
The constants below are defined by this extension, and will only be available when the extension has either been compiled into PHP or dynamically loaded at runtime.
Default DTD attributes
Load the external subset
Validate with the DTD
A recoverable error
A fatal error
No errors
A simple warning
Remove blank nodes
Merge CDATA as text nodes
Substitute entities
Suppress error reports
Disable network access when loading documents
Suppress warning reports
Remove redundant namespaces declarations
Implement XInclude substitution
libxml version like 20605 or 20617
libxml version like 2.6.5 or 2.6.17