According to the PHP documentation, there are a number of constants defined when the libxml extension is enabled.
These are accessible in the code, so something like
var_dump(LIBXML_DTDLOAD);
will return a value of int(4) (no problem so far, that's exactly what I expect to see)
What puzzles me is if I do
echo var_dump(defined(LIBXML_DTDLOAD));
I get a bool(false) returned....
So how can I access the constant and see its value if it isn't (apparently) defined? Or why does defined() return a false for a constant that clearly is defined?
You didn't quote the constant name
var_dump(defined('LIBXML_DTDLOAD')); // bool(true)