I was too eager to mark this as "done". There is still work left:
* "Disable on foo.com" should create a filter with flexible anchor
* Filter composer should be able to use flexible anchors (should that be the default for all suggestions?)
* Filter export from preferences should set ABP version to 1.1 if flexible anchors are found
Concerning flexible anchors at the end of the filter, I thought that the following definition would make sense:
foo|| means that "foo" should either be at the end of the address or it should be followed by a separator character. Separator characters are all characters but letters (need to recognize international letters somehow), digits, underscore, period, -, %. So || will be translated into something like:
So "||example.com||" will match "http://example.com/foo" and "http://example.com:1234/foo" but not "http://example.company.com/" and not "http://example.com.com/". Similarly "||example.com/foo||" will match "http://example.com/foo" and "http://example.com/foo/bar" but not "http://example.com/foobar".