There are several planning issues specific to TYPO3. Developers must take care of them before the actual development.
Each extension must have a unique key. Extension keys can be alphanumeric and contain underscore characters. It may not start with a digit, the letter
u, or the
test_ prefix. However, not every combination of these symbols makes a good extension key.
An extension key must be descriptive but not too long. Having personal or company prefixes is not forbidden but is not recommended. Underscores should be avoided. Abbreviations should be avoided as well, because they often do not make sense for other users.
Examples of bad extension keys are: