`@function`

Syntax

FunctionRule ::= '@function' <ident-token> ArgumentDeclaration '{' Statements '}'

No whitespace is allowed between the Identifier and the ArgumentDeclaration in FunctionRule.

To execute a @function rule rule:

Let name be the value of rule's Identifier.
If name begins with --, throw an error.
If name is calc, element, expression, url, and, or, or not, or if name has a vendor prefix and the unprefixed identifier is one of those strings, throw an error.
Let parent be the current scope.
Let function be a function named name which does the following when executed with args:
- With the current scope set to an empty scope with parent as its parent:
  - Evaluate args with rule's ArgumentDeclaration.
  - Execute each statement in rule.
  - Return the value from the @return rule if one was executed, or throw an error if no @return rule was executed.
If rule is outside of any block of statements:
- If name doesn't begin with - or _, set the current module's function name to function.
  
  This overrides the previous definition, if one exists.
- Set the current import context's function name to function.
  
  This happens regardless of whether or not it begins with - or _.
Otherwise, set the current scope's function name to function.