[cbolton]

I disagree with the assumption that the red/blue conflict should produce an error. In real life most of the time you want one style to override the other. So in this simplistic example at least, having the result determined by the order is the correct behavior (and it's what typst does).

More generally, if your system generates errors left and right, you end up making it hard for users to find a combination of packages that work. It's better to make them work error-free as much as possible. And the concept of "overriding" is natural and useful.

I think typst does make a nice attempt at managing global effects. It's nowhere near perfect but works pretty well already. For example it's super easy to implement your example with two packages, one applying bold and the other applying italic:

    Template from package A: #show regex("\bthe\b"): set text(style: "italic")
    Template from package B: #show regex("\bthe\b"): set text(weight: "bold")

You can use both templates in any order, typst will correctly render "the" in italic bold.