Mechanical errors

In response to my feedback on their essay, today a student asked me what ‘mechanical errors’ were. While it’s actually not that straight-forward to find a good definition online, I found a nice table that presents different categories of writing errors with their sub-categories. It is quite a useful schema to refer to when giving feedback (only skim-read the remainder of the article, so no endorsement — I’m in particular wondering what the authors mean by “Intelligible errors”, of which they seem to have found none ..).