Yes, that was common in the Spectrum and compatible computers.

You see that there are multiple words per key.

The exact one depends on the current input mode, so we would keep changing modes all the time.

That is also a reason why game developers with enough money would eventually get a 16 bit machine with UNIX, VMS or whatever, so that they would get a better development experience and then upload them via the extension port.

Here is an overview of it, https://retrocomputing.stackexchange.com/questions/3314/how-...

Yes, it's a version of ZX Spectrum. Each keyword had its own code in the character set.

Does this mean that these keys inserted actual instructions instead of a string of characters into the source code?

No, it was a mix of opcodes and text, from "The Complete 48K Disassembly"

"1B17: THE 'MAIN PARSER' OF THE BASIC INTERPRETER"

https://speccy.xyz/rom/asm/1b17

"1A48: THE SYNTAX TABLES"

https://speccy.xyz/rom/asm/1a48

You can read about "The Complete 48K Disassembly" on a recent HN post, https://news.ycombinator.com/item?id=23757449

Now, the Timex 2068 was a bit different, because its had more capabilities than the 48K, including a proper sound chip, the 48K compatibility was achieved via an extension Eprom.

Like these ones, https://k1.spdns.de/Vintage/Sinclair/Software/Timex%202068%2...