docs: complete calculated property support matrix

docs/en/low-code/expression-language.md

@@ -11,6 +11,8 @@ The Low-Code expression language is a provider-safe scalar profile used by virtu
 
 Expressions are not JavaScript. They cannot contain arbitrary code, SQL, network calls, browser APIs, side effects, or unsupported Power Fx table and record operations.
 
+An expression can contain up to 4096 characters.
+
 > **Preview:** The language profile is preview functionality. The supported syntax and function set may change before general availability.
 
 ## Values and field references
@@ -105,6 +107,13 @@ For a calculated property, the expression is expanded into the EF Core query. It
 
 For an ordinary property mapping that uses **Formula** existing-data backfill, the same scalar profile is compiled into a provider-side update that initializes existing rows once. The mapped property then stores the result; this is separate from a virtual calculated property.
 
+During JSON-to-database mapping, use `Self` to read the property's current JSON value before it is moved to the database column:
+
+```text
+Coalesce(Self, "Unknown")
+Self & " migrated"
+```
+
 Related-record aggregates are not written inside a formula expression. Create a [Rollup Property](formula-properties.md#create-a-rollup-property) for `Count`, `Sum`, `Average`, `Min`, or `Max` over related records.
 
 ## Validation errors

docs/en/low-code/formula-properties.md

@@ -49,6 +49,8 @@ Client applications cannot set a calculated property. Enable **Server only** whe
 
 A rollup evaluates a correlated aggregate over related records. For example, an `Order` can expose the sum of `OrderItem.LineTotal` values when `OrderItem.OrderId` is a foreign key to `Order`.
 
+`Sum` is a rollup operation, not a function that can be written inside a scalar formula. The relationship is evaluated in the reverse direction: the source entity contains the foreign key that points to the entity receiving the rollup.
+
 1. Open **Add Property** and select **Rollup Property**.
 2. Select the **Source Entity** that contains the related records.
 3. Select the **Relation Field** whose foreign key points to the current entity.
@@ -56,7 +58,14 @@ A rollup evaluates a correlated aggregate over related records. For example, an
 5. For every operation except `Count`, select the **Value Field**.
 6. Review validation and select **Create Rollup Property**.
 
-`Count` returns a Long value and does not use a value field. `Sum` and `Average` require a numeric value field. `Min` and `Max` preserve a compatible scalar type. A rollup value may be a normal field or a formula property, but it cannot be another rollup.
+| Operation | Value field | Result |
+| --- | --- | --- |
+| `Count` | Not used | Long |
+| `Sum` | Int, Long, Decimal, or Money | Preserves a compatible numeric range |
+| `Average` | Int, Long, Decimal, or Money | Decimal, or Money for a Money value |
+| `Min` / `Max` | String, Int, Long, Decimal, Money, Boolean, Date, or DateTime | Preserves a compatible scalar type |
+
+A rollup value may be a normal field or a formula property, but it cannot be another rollup. Formulas can reference other calculated properties, including rollup results, and the complete dependency graph is validated for cycles and provider translation.
 
 ## Storage and query behavior
 

docs/en/low-code/index.md

@@ -109,8 +109,8 @@ The screens below follow that common designer flow from data to page setup to fo
 
 ![Page setup in the designer](images/designer-page-filters.png)
 
-![Form setup in the designer](images/designer-forms.png)
-
+![Form setup in the designer](images/designer-forms.png)
+
 For virtual fields calculated from the current record, related records, or related-record aggregates, see [Calculated and Rollup Properties](formula-properties.md). For the provider-safe scalar syntax used by calculated properties and formula backfills, see the [Low-Code Expression Language](expression-language.md) reference.
 
 ## React Runtime