Of course, extensions can also be implemented directly in the Zend
engine. This strategy is good if you need a change in the language behavior or require
special functions to be built directly into the language core. In general, however, modifications to the
Zend engine should be avoided. Changes here result in
incompatibilities with the rest of the world, and hardly anyone will ever adapt
to specially patched Zend engines. Modifications can't be detached from the
main PHP sources and are overridden with the next update using the
"official" source repositories. Therefore, this method is generally considered bad practice and, due
to its rarity, is not covered in this book.
