In Eclipse (3.3) if you start the New Plugin Project Wizard, the first page has a Target Platform, where you can target a version of eclipse.
Is this information saved/used and if so where?
Also if you then create an extension the plugin.xml is created, and at the top is (for me) :
<?eclipse version="3.2"?>
Where did this version come from?, does it depend on the extension you just extended? Will it be updated/changed?
The plugin 3.2 version is there because there were changes prior to 3.2 which would make it incompatible. However, it's remained the same from 3.2 onwards.
You'll also find that it records the information in the MANIFEST.MF in the Required Execution Environment and (for OSGi apps) puts specific versions in the org.osgi.framework or org.eclipse.core dependencies.
So there's a subtle mapping between Eclipse version and what version numbers are put in these entires; it's not just a 1-1 correspondence between the two.