Users with large backups may be unaware that their backups are saved as one giant JSON array. In this case mongoimport may try reading that entire array as a single JSON document (i.e., with a top-level array), which almost certainly will not be what the user wants and may cause memory-consumption problems besides.

mongoimport should, if the first JSON character is `[` but the user did not pass the `--jsonArray` flag, show a warning to the effect of:

$filename begins with `[`, but you didn’t pass --jsonArray. Did you mean to?