docs(guide): named columns vs structured references (SU-637)

docs/guide/cell-references.md

@@ -204,7 +204,7 @@ You can reference ranges:
 
 The following restraints apply:
 - You can't mix two different types of range references together (=A1:B).
-- Range expressions can't contain [named expressions](/guide/named-expressions.md).
+- Range expressions can't contain [named expressions](/guide/named-expressions.md) (`=Name_1:Name_5` is a parse error). To name a whole column, see [Named columns](/guide/named-expressions.md#named-columns).
 - At the moment, HyperFormula doesn't support multi-cell range references (=A1:B2:C3).
 
 ::: tip

docs/guide/named-expressions.md

@@ -4,6 +4,7 @@ tags:
   - global scope
   - variables
   - named constants
+  - structured references
   - addNamedExpression
   - changeNamedExpression
   - removeNamedExpression
@@ -83,6 +84,7 @@ For examples of valid and invalid expression names, see the following table:
 | ASP.NET     | Valid    |
 | A1          | Invalid  |
 | $A$1        | Invalid  |
+| Name1       | Invalid  |
 | RC          | Invalid  |
 
 ## Using named expressions in formulas
@@ -114,6 +116,28 @@ When array arithmetic is enabled (`useArrayArithmetic: true`), named ranges stil
 - A bare `=myRange + 1` does not spill — it returns a `#VALUE!` error rather than producing one result per element.
 - Inside an aggregate the operator becomes element-wise. `=SUM(myRange + 1)` adds 1 to every element and then sums, so for `myRange` covering values `1..5` it returns `20` (`SUM(2, 3, 4, 5, 6)`), not the single reduced value of the default mode.
 
+## Named columns
+
+To address a column by name, register a named expression that points at the column (or at the data range), then use that name in the formula:
+
+```javascript
+hfInstance.addNamedExpression('ColSales', '=Sheet1!$A:$A');
+hfInstance.setCellContents({ sheet: 0, col: 2, row: 0 }, [['=SUM(ColSales)']]);
+```
+
+- The address inside the named expression must be **absolute** (`$A:$A` or `Sheet1!$A:$A`). Relative `A:A` is not allowed.
+- If row 1 is a header, `$A:$A` includes it. For data only, use `$A$2:$A`.
+- Do not put header text in the formula. Map each header to a named expression in application code.
+
+### Why SUM(Name1:Name5) does not work
+
+HyperFormula does not support Excel-style structured references such as `Table[Column]`, and it does not treat column headers as formula addresses. A formula like `=SUM(Name1:Name5)` is not a reference to columns named Name1 and Name5.
+
+Two separate problems often get stacked in that example:
+
+1. **Illegal name.** `Name1` matches A1 notation (column NAME, row 1), so it cannot be registered as a named expression. Use `ColSales` or `Name_1` instead. See [Naming rules](#naming-rules).
+2. **Range operator.** `:` does not accept named expressions as endpoints. Even with legal names, `Name_1:Name_5` is a parse error. See [Range restraints](cell-references.md#range-restraints).
+
 ## Available methods
 
 These are the basic methods that can be used to add and manipulate named