Can Stylus :extend reliably preserve selector order and pseudo-classes across versions?

Goal

We need a repeatable development environment that guarantees deterministic CSS output when using Stylus’s :extend directive. The goal is to understand how selector ordering, mixin defaults, pseudo‑classes, and media queries interact across major Stylus releases (2.7.x vs. 3.0.x).

Constraints & Uncertainty

The current documentation does not specify whether :extend merges selector lists in a stable order, or whether the order can change when multiple extensions are applied. Additionally, it is unclear if extending a selector that contains a mixin with default arguments preserves those properties, and whether pseudo‑classes defined in a separate file survive the extension. Media queries attached to selectors may also be reordered, affecting cascade priority.

Specific Questions

1. Which ordering does Stylus use for selectors from extended rules when multiple :extend directives are combined across 2.7.x and 3.0.x?
2. Does extending a selector that contains a mixin with default arguments preserve the mixin’s properties in both 2.7.x and 3.0.x?
3. When extending a selector with pseudo‑classes defined in a different file, does Stylus retain the pseudo‑class in the compiled CSS?
4. Will a media query stay attached to the extended selector or be appended after the selector list, altering cascade order?