Question about license implications of embedding Tectonic (esp. engine_xdvipdfmx)

[hahnlee]

Hello, first of all, thank you for this amazing project — I deeply respect the amount of work and care that's gone into it.
That said, I have a question that I’m having trouble figuring out:

I understand that Tectonic itself is under the MIT license. However, as stated in the LICENSE file:

Elements of the system from which it is derived are licensed under an extremely wide variety of open-source licenses.

In particular, I noticed that the engine_xdvipdfmx crate appears to include source code from (x)dvipdfmx. Given this, I’m wondering:

If I embed Tectonic (e.g., as a library in my own application), would this cause any GPL-style copyleft implications — especially due to the licensing of the original (x)dvipdfmx code?

I want to make sure I'm not inadvertently triggering any license incompatibilities or viral licensing effects by using Tectonic in this way.