I would imagine this support to be stomachable if it was active at all times but using a visually different syntax for 0-based and 1-based indexing, maybe using something like the guillemet for the latter (like this: «1») that is wild enough to draw the user's attention when reading the code, and not common/prominent enough across keyboard layouts to make most users think twice before using it when writing code unless it makes sense for the domain.

[1] https://stackoverflow.com/questions/48562873/zero-indexed-ar...

You could declare the array as array[0..100] of something resp. array[1..100] of something for 0/1 based, and just as well do array[2..100] of something, or array[-1..100] of something, for -1/2 based.

Or with letters array['a'..'z'] of something,

Or with enums. TEnum = (red, blue, green), and then an array array[red..green] of something

Actually, that is just Pascal

Matrix operations were first class.