[beagle3]

> I would've liked it better if it forced tabs, that way you'd have one tab for one indentation level, and everyone could choose their own preference of indentation.

The problem with this is that in many code bases, you occasionally need spaces to align code/data in different lines to make them more readable and easily inspectable, e.g. within a long parenthesized expression spanning multiple lines. In that case, indentation tabs require nontrivial gymnastics, whereas spaces are consistent.

The files should always contain spaces - because behaving as if spaces are tabs is round-trippable even when every user uses a different setting. An editor could en-tab on load, de-tab on save, and everyone is happy (though I'm not aware of any editor that does this). If the file only has tabs, the converse "de-tab on load and en-tab on save" does not give you the same alignment flexibility.