Check how big effort is required to make it compatible with other "Expect" implementations

The following would be nice:
- `send()` function (alias to either `write()` or `puts()`)
- check how incompatible is our `expect()`

Start by locating the existing PTY interaction entry points for `write()`, `puts()`, and `expect()`, then review how comparable Expect implementations behave. Done means the effort to add `send()` and assess `expect()` compatibility is documented with the relevant incompatibilities and scope identified.

Written by the indexing model from the issue text.