@cname currently refers to the constant name in C. However, it is not always a (constant) name, but sometimes a function invocation, so naming it as @cvalue would be more appropriate.
This method was used to protect code against XXE processing attacks.
Since PHP now requires libxml >= 2.9.0 external entity loading no longer
needs to be disabled to prevent these attacks. It is disabled by default.
Also, the method has an unwanted side effect that causes a lot of
confusion: Parsing XML data from resources like files is no longer possible.
Closes GH-5867.
