Meaning and meant as a general rule as long as you keep your modification to eZ Publish within the above directories; Inside these directories is acceptable and not a hack. Anything within the 'extension' directory is considered an extension, separate and not a hack; even if you don't activate it or use it like a traditional extension.

* Note: 'var/', modifications are allowed and often required. eZ Publish Packages relies on storing package contents within the var/ directory. For example, eZ Publish Site Design Packages, relies storing package contents like css in the var/ directory for design modifications.

Example Directories

bin
cronjobs
design
doc
kernel
lib
packages
share
support
update

Exceptions

I'm sure there are extensions to these general rules and guidelines. This document is a guide not an absolute.

Patch extensions

Extensions which contain kernel patches where required to impliment a feature that must be added to the kernel. This is rare that most people need to do this but it is known to exist.

References

Kernel Hacking