In #63 (comment) it was stated that

This library only supports the original contrab expression. [...] A first Tueday of a month can only occur on days 1-7, so you could use the 0 8 1-7 * Tue expression to effectively get 8 AM on first seven days of any month that's a Tuesday.

However, according to the crontab manpage:

Note: The day of a command's execution can be specified in the
following two fields — 'day of month', and 'day of week'. If
both fields are restricted (i.e., do not contain the "*"
character), the command will be run when either field matches the
current time. For example,
"30 4 1,15 * 5" would cause a command to be run at 4:30 am on the
1st and 15th of each month, plus every Friday.

Applied to the first example above, 0 8 1-7 * Tue, that would be "At 08:00 on every day-of-month from 1 through 7 and on Tuesday.", which is also confirmed by crontab.guru.

There's a detailed blog post about this and some funky way to work around it, but these workarounds produce exceptions in this library.

I don't think this is something that is easy to fix without breaking clients, and something that perhaps shouldn't be fixed, since it's more of a quirk in the original syntax. However, for me this was quite unexpected and I wasn't able to find much information about it, so I thought it might be worth pointing out, in case it should be included in the documentation.