[css-namespaces-3] Clarify the validity of @namespace preceding @import

[cdoublev]

Any @namespace rules must follow all @charset and @import rules and precede all other non-ignored at-rules and style rules in a style sheet. [...]

A syntactically invalid @namespace rule (whether malformed or misplaced) must be ignored.

https://drafts.csswg.org/css-namespaces-3/#syntax

In the following case, both Chrome/Firefox do not ignore @namespace but ignore the @import:

<style>
  @namespace test "http://www.w3.org/2000/svg";
  @import "./stylesheet.css"; /* Declares `div { color: green }` */
  test|svg {
    background-color: red;
  }
</style>
<div>Green?</div>
<svg width="500" height="500"></svg>

A strict interpretation would be that @namespace is misplaced and should be ignored.

Also, I did not test the current UA behavior with @namespace preceding @charset, but I understood that all other rules following the first @charset rules are ignored, therefore it could be allowed.

User agents must ignore any @charset rule not at the beginning of the style sheet. When user agents detect the character encoding using the BOM and/or the @charset rule, they should follow the following rules:

Except as specified in these rules, all @charset rules are ignored.

https://drafts.csswg.org/css2/#charset%E2%91%A0

EDIT: @import would be invalid (see below) and ignored, @charset not at the beginning of the style sheet is also ignored (see above), and @namespace is valid if it precedes all other non-ignored at-rules, ie. any valid rules that is not @import (again, @charset following @namespace is always invalid).

Any @import rules must precede all other valid at-rules and style rules in a style sheet (ignoring @charset), or else the @import rule is invalid