If you have your PECL code in the PHP CVS repository, you need to be aware of our branching convention. The PHP core code is branched like this:

------------------------------------ HEAD (development)
    \               \
     \               ---- PHP_5_0 (stable)
      --- PHP_4_3 (stable)

All development takes place on HEAD, and important bug fixes are then backported to the stable branch(es) when appropriate. In general, no new features are added to the stable branches.

The convention for PECL extensions is to use a similar (but not identical!) scheme, in order to more easily coexist with some magic in the repository and with snapshot building tools:

------------------------------------ HEAD (development)
    \               \
     \               ---- PECL_5_0 (stable)
      --- PECL_4_3 (stable)

You only need to create/maintain these branches if the PHP core is branched for release and HEAD (of both your code and the core) is changing in a backwards incompatible way, so that it would not be possible to compile your code against the release branch anymore.

You don't need to branch if your code on HEAD has appropriate #ifdef's to allow it to compile with the different PHP versions.

You also don't need to branch if you don't intend to maintain your extension for those older versions; make sure you publish a version specific PECL package before dropping support for a release.