Explicitly define FunctionExpression

This sets the stage for modifying it to fix #3245

spec/syntax.md

@@ -9,6 +9,7 @@
   * [`InterpolatedIdentifier`](#interpolatedidentifier)
   * [`InterpolatedUrl`](#interpolatedurl)
   * [`Name`](#name)
+  * [`FunctionExpression`](#functionexpression)
   * [`SpecialFunctionExpression`](#specialfunctionexpression)
   * [`PseudoSelector`](#pseudoselector)
 * [Procedures](#procedures)
@@ -71,6 +72,30 @@ No whitespace is allowed between components of an `InterpolatedUnquotedUrlConten
 [identifier code point]: https://drafts.csswg.org/css-syntax-3/#identifier-code-point
 [escape]: https://drafts.csswg.org/css-syntax-3/#escape-diagram
 
+### `FunctionExpression`
+
+<x><pre>
+**FunctionExpression**¹ ::= [CssMinMax]
+&#32;                     | SpecialFunctionExpression
+&#32;                     | [CalculationExpression]
+&#32;                     | FunctionCall
+**FunctionCall**        ::= FunctionName FunctionArguments ')'
+**FunctionName**²       ::= [NamespacedIdentifier] '('
+</pre></x>
+
+[CssMinMax]: types/calculation.md#cssminmax
+[CalculationExpression]: types/calculation.md#calculationexpression
+[NamespacedIdentifier]: modules.md#syntax
+
+1: If both `CssMinMax` and `FunctionCall` could be consumed, `CssMinMax`
+   takes precedence.
+
+2: `FunctionName` may not contain any whitespace, may not match
+   [`SpecialFunctionName`], and may not be case-insensitively equal to `'calc('`
+   or `'clamp('`.
+
+[`SpecialFunctionName`]: #specialfunctionexpression
+
 ### `SpecialFunctionExpression`
 
 > These functions are "special" in the sense that their arguments don't use the

spec/types/calculation.md

@@ -4,7 +4,7 @@
 
 * [Syntax](#syntax)
   * [`CalculationExpression`](#calculationexpression)
-  * [`MinMaxExpression`](#minmaxexpression)
+  * [`CssMinMax`](#cssminmax)
 * [Types](#types)
   * [Operations](#operations)
     * [Equality](#equality)
@@ -18,7 +18,7 @@
 * [Semantics](#semantics)
   * [`CalcExpression`](#calcexpression)
   * [`ClampExpression`](#clampexpression)
-  * [`CssMinMax`](#cssminmax)
+  * [`CssMinMax`](#cssminmax-1)
   * [`CalcArgument`](#calcargument)
   * [`CalcSum`](#calcsum)
   * [`CalcProduct`](#calcproduct)
@@ -73,21 +73,13 @@ case-insensitively.
 > expression regardless of syntax, for full compatibility it's necessary to
 > parse it very expansively.
 
-### `MinMaxExpression`
-
-This production is parsed in a SassScript context when an expression is expected
-and the input stream starts with an identifier with value `min` or `max`
-(ignoring case) followed immediately by `(`.
+### `CssMinMax`
 
 <x><pre>
-**MinMaxExpression**¹ ::= CssMinMax | FunctionExpression
-**CssMinMax**         ::= ('min(' | 'max(')² CalcArgument (',' CalcArgument)* ')'
+**CssMinMax**         ::= ('min(' | 'max(')¹ CalcArgument (',' CalcArgument)* ')'
 </pre></x>
 
-1: If both `CssMinMax` and `FunctionExpression` could be consumed, `CssMinMax`
-   takes precedence.
-
-2: The strings `min(` and `max(` are matched case-insensitively.
+1: The strings `min(` and `max(` are matched case-insensitively.
 
 ## Types