sass/spec/at-rules/unknown.md

Unknown At-Rules

Syntax

In order to be flexible in its compatibility with future additions to CSS, Sass supports all at-rule names with a default syntax that's highly liberal in the structures it allows.

UnknownAtRule ::= '@' InterpolatedIdentifier InterpolatedValue?
                    ('{' Statements '}')?

No whitespace is allowed after @. As with all statements, an UnknownAtRule without a block must be separated from other statements with a semicolon.

Semantics

To execute an unknown at-rule rule:

• Let name be the result of evaluating rule's InterpolatedIdentifier.

• Let value be the result of evaluating rule's InterpolatedValue, if it exists.

• Let css be a CSS unknown at-rule with name name, value value, and with an empty list of children if rule has Statements.

• Let parent be the current style rule, keyframe block, or at-rule if one exists; or the innermost if multiple exist.

• If rule has Statements:

  • If parent isn't set, append css to the current module's CSS.

  • Otherwise, if parent is a style rule:

    • If rule's name is "font-face", or if its unprefixed name is "keyframes", append css to the current module's CSS.

    • Otherwise:

      • Append css to parent's parent.

      • Append a copy of parent without any children to css.

        This copy is now the current style rule until rule is done being executed.

  • Otherwise, append css to parent.

  • Evaluate each child in rule's Statements.

• Otherwise:

  • Append css to parent if it's set, or to the current module's CSS otherwise.