No, there is no facility for variable templating, interpolation, references, or anything of the like in toml.
If you wanted that, you could implement it in your application by doing post-processing on strings, or you could not use TOML.
> What is the keyword for null?
If you have "x = 1", you can always comment it out with "# x = 1". There's no specific support for null.
it would be kinda silly to have it anyways since null is a language construct more than anything else, and e.g. some lanuages support mixed strings + nulls in one array, but many don't.
- Is interpolation supported? e.g. "key1" = "value" and then "key2" = "$key1". That would be very useful in avoiding repetition.
- What is the keyword for null? e.g. when I want to set the value to null