Understand foreign function interface (FFI) and language binding

Mixing different programming languages has long been something I don't quite understand. According to this Wikipedia article, a foreign function interface (or FFI) can be done in several ways:

1. Requiring that guest-language functions which are to be host-language callable be specified or implemented in a particular way; often using a compatibility library of some sort.
2. Use of a tool to automatically "wrap" guest-language functions with appropriate glue code, which performs any necessary translation.
3. Use of wrapper libraries
4. Restricting the set of host language capabilities which can be used cross-language. For example, C++ functions called from C may not (in general) include reference parameters or throw exceptions.

My questions:

1. What are the differences between the 1st, 2nd and 3rd ways? It seems to me they are all to compile the code of the called language into some library with object files and header files, which are then called by the calling language.

2. One source it links says, implementing an FFI can be done in several ways:

   • Requiring the called functions in the target language implement a specific protocol.
   • Implementing a wrapper library that takes a given low-language function, and "wraps" it with code to do data conversion to/from the high-level language conventions.
   • Requiring functions declared native to use a subset of high-level functionality (which is compatible with the low-level language).

   I was wondering if the first way in the linked source is the same as the first way in Wikipedia?

   What does the thir