Wrappers so you can use all the Java Runtime Environments with their slightly incompatible APIs with more ease.
Used to use an over-engineered "plugin" mechanism although there was only one "plugin", called "sunmajor", that handles all possible JREs.
IMPORTANT: The <updated> element in vmfwk/distributions/OpenOfficeorg/javavendors_*.xml files should only be updated for incompatible changes, not for compatible ones. As stated in the commit message of https://gerrit.libreoffice.org/#/c/69730/ in LibreOffice gerrit:
javavendors_*.xml <updated> should not have been updated...
Changing <updated> causes jfw_startVM and jfw_getSelectedJRE (both jvmfwk/source/framework.cxx) to fail with JFW_E_INVALID_SETTINGS, which in turn causes functionality that requires a JVM to issue a GUI error dialog stating that the user must select a new JRE in the Options dialog. While that behavior makes sense if a JRE was selected that would no longer be supported by the modified javavendors_*.xml, it is just annoying if an already selected JRE is still supported. And a compatible change to javavendors_*.xml implies that an already selected JRE will still be supported."