Choosing the PHP version

With new product versions, Plesk adapts current versions of PHP.
Therefore, it is important to correctly choose the version of PHP for
developing your extension. The following table shows the recent Plesk
product versions and the corresponding versions of PHP.

First, you need to decide what versions of Plesk you want your extension
to support. Keep in mind the following:

• The more Plesk product versions are supported, the wider the audience
  for your extension.
• The more Plesk product versions are supported, the less advanced SDK
  is available for you, since you would have to use the one for the
  earliest version of Plesk you plan to support.

Second, based on the selected range of Plesk product versions, you need
to choose the suitable PHP version. Important considerations:

• To ensure that all the selected Plesk product versions are supported,
  you should select the version of PHP that corresponds to the earliest
  selected Plesk version.
• While new versions of PHP retain backward compatibility, keep in mind
  that sometimes incompatible changes are introduced. Refer to the PHP
  documentation to ensure that you are not using elements that are
  deprecated in more recent versions.

For example, consider making an extension that supports both Plesk 17.5
and Plesk 17.8. Plesk 17.5 uses PHP 5.6, and Plesk 17.8 uses PHP 7.1. To
support both, the extension should use the earliest version of PHP,
which is 5.6 in this case, and the Plesk 17.5 SDK. Additionally, the
extension should not use certain deprecated elements from 5.6, which
were dropped in 7.1.

Finally, the completed extension must be thoroughly tested on all Plesk
product versions that are supported to make sure it works correctly and
is not influenced by differences in engines and SDK versions.