In American English, "which" is supposed to be non-restrictive if not followed by a preposition. At least if I remember it correctly. (I'm a Slavic person speak

In American English, "which" is supposed to be non-restrictive if not followed by a preposition. At least if I remember it correctly. (I'm a Slavic person speaking an L2 English interlanguage, not native English, so I may be wrong.) Also, it seems to be a nice example of something that would require a substantial level of natural language understanding from the style checker in order to be detectable (or, as is the current fashion, at least a really substantial body of statistical data).