The Zend API has evolved considerably over time, as PHP has become a more
robust and widespread language. With the introduction of PHP 5 came the
Zend Engine 2 (ZE2). ZE2 came with an almost entirely new Object-Oriented
Programming (OOP) model, as well as improvements in most aspects of the
API. PHP 6, which is still under active development at the time of this
writing, introduces the Zend Engine 3 (ZE3), which brings full Unicode
support to the language.
This documentation is still under heavy development. The original Zend
documentation is preserved in its entirety in the
Zend Engine 1 section for those who
need it before this documentation is completed.
This section of the manual is devoted to ZE2. While PHP 4.4 is still in
widespread use, the differences in how extensions are written in ZE1 are
small; a short reference to them is given in an appendix to this section.
ZE3's API may yet change significantly, and is covered in another appendix.
It will be more fully documented when PHP 6 enters a beta testing stage.
The documentation in this section is current as of PHP 5.2.5, the most
recent stable release at the time of this writing. Notable differences in
the minor PHP 5 releases (5.0 through 5.3) are given as appropriate.