I have discovered (by asking my question here) that Slim needs PHP 5.6 as line 299 is part of a try/catch/finally structure where the finally keyword made its appearance in PHP 5.5. There may be other parts of Slim that justifies it’s stated requirement for PHP 5.6. I have not yet found any other part of OJS3.1.0 that has PHP 5.6 specific coding - but still looking.
The XML error will need to have the document being imported examined where indicated.