feat(pages): write DynamicClasses and DynamicCellClass as expressions (#750)

.claude/skills/mendix/alter-page/SKILL.md

@@ -470,21 +470,27 @@ Property names resolve against the keys the installed widget declares, so both
 the schema key and mxcli's MDL alias work (`DynamicCellClass` and `ColumnClass`
 both reach `columnClass`). An unknown name lists what *is* settable on that grid.
 
-**Expression-valued properties take a Mendix expression, not a literal.**
-`DynamicCellClass` and `Visible` are expressions, so a literal CSS class has to be
-a quoted string *inside* the expression — doubled quotes in MDL:
+**`DynamicCellClass` (and a widget's `DynamicClasses`) take a Mendix expression,
+written as-is.** A quoted value is a Mendix string, so a literal CSS class is just
+the quoted class name, and a computed one is the expression itself:
 
 ```mdl
--- WRONG: the expression becomes a bare identifier, mxbuild reports CE0117
+-- a literal class: the string 'highlight'
 alter page Mod.P { SET DynamicCellClass = 'highlight' ON dg1.Label }
 
--- correct: the expression is the string literal 'highlight'
-alter page Mod.P { SET DynamicCellClass = '''highlight''' ON dg1.Label }
+-- a computed class
+alter page Mod.P { SET DynamicCellClass = if $currentObject/Price > 100 then 'highlight' else '' ON dg1.Label }
+
+-- WRONG: a bare name is an identifier, not a string — mxbuild reports CE0117
+alter page Mod.P { SET DynamicCellClass = highlight ON dg1.Label }
 ```
 
-This applies equally to `create page`; the two paths behave identically. A bare
-identifier is not a valid Mendix expression, and mxbuild reports CE0117 against
-the column.
+The old spelling — the expression's text in quotes, `'if … then ''a'' else '''''`
+— is refused as MDL-WIDGET33, because it would now store that text as a class
+name. This applies equally to `create page`; the two paths behave identically.
+
+A column's pluggable `Visible` expression is not converted yet: there a quoted
+value is still the expression's text, so a literal needs the doubled quotes.
 
 Properties holding a **structured** value — `attribute`, `filter`, `content`,
 actions — cannot be set by ALTER at all. It refuses them and points at

.claude/skills/mendix/create-page/SKILL.md

@@ -134,26 +134,29 @@ actionbutton btn (caption: 'Save', designproperties: ['Size': 'Large', 'Full wid
 ```
 
 **Dynamic Classes** — a Mendix expression evaluated at runtime that returns a
-class list (applied on top of the static `class`). Root attributes in
-`$currentObject` and escape single quotes by doubling them (`''`):
+class list (applied on top of the static `class`). Write the expression as-is —
+no outer quotes, no doubled ones — and root attributes in `$currentObject`. A
+quoted value is a Mendix string: `dynamicclasses: 'is-featured'` is the class
+`is-featured`.
 ```sql
 dynamictext ovChip (
   content: 'chip',
   class: 'ss-chip',
-  dynamicclasses: 'if $currentObject/VesselClass = Mod.BoatClass.Astute then ''ss-chip--astute'' else '''''
+  dynamicclasses: if $currentObject/VesselClass = Mod.BoatClass.Astute then 'ss-chip--astute' else ''
 )
 ```
 
-Write it quoted, not in brackets: `dynamicclasses: [ … ]` (and a column's
-`DynamicCellClass: [ … ]`) parses as a list, which no writer reads — `check`
-reports it as MDL-WIDGET32 rather than letting the value be dropped.
+Not in brackets: `dynamicclasses: [ … ]` (and a column's `DynamicCellClass: [ … ]`)
+parses as a list, which no writer reads — `check` reports it as MDL-WIDGET32. And
+not the old quoted spelling `'if … then ''a'' else '''''`, which would now store
+the expression's text as a class name — `check` reports it as MDL-WIDGET33.
 
 **All can be combined on a single widget:**
 ```sql
 container ctnHero (
   class: 'card',
   style: 'border-left: 4px solid #264AE5;',
-  dynamicclasses: 'if $currentObject/Featured then ''is-featured'' else ''''',
+  dynamicclasses: if $currentObject/Featured then 'is-featured' else '',
   designproperties: ['Spacing top': 'Large', 'Full width': on]
 ) {
   dynamictext txtTitle (content: 'Styled Container', rendermode: H3)

.claude/skills/mendix/create-page/reference/widgets.md

@@ -340,7 +340,7 @@ column colPrice (
   Sortable: false, Resizable: false,
   Hidable: hidden,
   ColumnWidth: manual, Size: 150,
-  DynamicCellClass: 'if($currentObject/Price > 100) then ''highlight'' else '''' ',
+  DynamicCellClass: if($currentObject/Price > 100) then 'highlight' else '' ,
   tooltip: 'Price in USD'
 )
 ```

.claude/skills/mendix/migrate-design-prototype/SKILL.md

@@ -501,13 +501,13 @@ top of** `Class:`.
 ```sql
 container heatCell (
   Class: 'ss-heat-cell',
-  DynamicClasses: 'if $currentObject/M01 >= 100 then ''ss-heat--over''
-                   else if $currentObject/M01 >= 80 then ''ss-heat--warn''
-                   else ''ss-heat--ok'''
+  DynamicClasses: if $currentObject/M01 >= 100 then 'ss-heat--over'
+                   else if $currentObject/M01 >= 80 then 'ss-heat--warn'
+                   else 'ss-heat--ok'
 )
 ```
 
-(Note the doubled single-quotes for string literals inside an MDL expression.)
+(Written as-is: plain single quotes inside, no outer quotes around the expression.)
 
 ### Computed dimensions — the bucket-class idiom
 
@@ -526,7 +526,7 @@ bucket and generate one class per bucket**:
 ```
 
 3. Select the class from the bucket:
-   `DynamicClasses: '''ss-pb-'' + toString($currentObject/PctBucket)'`.
+   `DynamicClasses: 'ss-pb-' + toString($currentObject/PctBucket)`.
 
 Trade-off worth noting: this adds one bucket attribute per animated dimension to the
 domain model. Pick a bucket count that matches the visual precision you need (20 → 5%

CHANGELOG.md

@@ -8,6 +8,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
 
 ### Changed
 
+- **`DynamicClasses` and a column's `DynamicCellClass` are written as Mendix expressions** (mendixlabs/mxcli#750) — the expression is written as-is, so the doubled-quote spelling is gone: `dynamicclasses: if $currentObject/Featured then 'is-featured' else ''`, and `dynamicclasses: 'is-featured'` is the string — the class `is-featured`. The same rule as the OData client's credentials. `create page`, `alter page … set` and `describe` all use it, and a describe → exec round trip stores identical values (measured on a Mendix 11.14.0 project). **Migrating a script:** the old spelling, the expression's text in quotes (`'if … then ''a'' else '''''`), still parses but would now store that text as a class name, so `check` and `exec` refuse it as **MDL-WIDGET33** and give the unquoted expression. An expression in any other widget property is an error rather than an empty value; a pluggable property whose schema kind is Expression (a column's `Visible`, for one) keeps the quoted form until a following change.
 - **An OData client's credentials and header values are written as Mendix expressions** (mendixlabs/mxcli#750) — `HttpUsername`, `HttpPassword`, `ClientCertificate` and every `headers (…)` value hold an expression, and MDL now writes it as-is: `HttpUsername: 'admin'` is the string `'admin'`, `@Module.Const` reads a constant, and `'Bearer ' + @Module.Token` concatenates. Before, a quoted value was the expression's *text*, so `'admin'` stored the identifier `admin` and a string needed `'''admin'''`. `describe` prints the stored expression as-is, so Studio Pro's `'abc'` now reads `HttpUsername: 'abc'`; measured against a Studio Pro-authored client, and a describe → exec round trip stores identical values. **Migrating a script:** `'''admin'''` becomes `'admin'`, and a quoted constant `'@Module.Const'` becomes `@Module.Const` — both old forms still parse but would now store something else, so `check` and `exec` refuse them as **MDL-ODATA07**. A compound expression in any other OData property (`Path: 'a' + 'b'`) is an error rather than an empty value. `ServiceUrl` is a constant reference, not an expression — see the next entry.
 - **An OData client's `ServiceUrl` names a constant, like `ProxyHost`** (mendixlabs/mxcli#750) — Studio Pro picks the service URL as a constant and stores it as `@Module.Name`. `ServiceUrl: Module.Location` is now accepted alongside `@Module.Location` and `'@Module.Location'` (the bare name used to be refused as "not a constant reference"); all three store the same value, and `describe` prints the bare name, as it does for the proxy references. A literal URL is still refused (CE6825).
 

cmd/mxcli/syntax/features_page.go

@@ -317,7 +317,7 @@ CREATE PAGE Sales.Detail (Title: 'Detail', Layout: Atlas_Core.Atlas_Default) {
 			"Reach for ALTER STYLING rather than CREATE OR REPLACE PAGE whenever only\n" +
 			"the look changes: replacing the page rewrites every widget in it, so the\n" +
 			"diff is the whole document and anything MDL cannot yet spell is lost.",
-		Example: "CONTAINER ctn (\n  Class: 'my-card',\n  DynamicClasses: 'if $currentObject/Priority = ''High'' then ''card-danger'' else ''card-normal'''\n) {\n  DYNAMICTEXT txt (Content: 'Styled text')\n}\n\n" +
+		Example: "CONTAINER ctn (\n  Class: 'my-card',\n  DynamicClasses: if $currentObject/Priority = 'High' then 'card-danger' else 'card-normal'\n) {\n  DYNAMICTEXT txt (Content: 'Styled text')\n}\n\n" +
 			"-- Restyle one widget on a page that already exists\n" +
 			"alter styling on page Sales.OrderOverview widget btnSave\n" +
 			"  set Class = 'btn-primary', 'Spacing top' = 'Large';\n\n" +

docs-site/src/appendixes/quick-reference.md

@@ -359,7 +359,7 @@ MDL uses explicit property declarations for pages:
 | Selection binding | `DataSource: SELECTION widget` | `DATAVIEW dv (DataSource: SELECTION galleryList)` |
 | CSS class | `Class: 'classes'` | `CONTAINER c (Class: 'card mx-spacing-top-large')` |
 | Inline style | `Style: 'css'` | `CONTAINER c (Style: 'padding: 16px;')` |
-| Dynamic classes | `DynamicClasses: 'expr'` | `CONTAINER c (DynamicClasses: 'if $currentObject/IsActive then ''is-active'' else ''''')` — runtime-computed; stacks on `Class` |
+| Dynamic classes | `DynamicClasses: 'expr'` | `CONTAINER c (DynamicClasses: if $currentObject/IsActive then 'is-active' else '')` — runtime-computed; stacks on `Class` |
 | Design properties | `DesignProperties: [...]` | `CONTAINER c (DesignProperties: ['Spacing top': 'Large', 'Full width': ON])` |
 | Width (pixels) | `Width: integer` | `IMAGE img (Width: 200)` |
 | Height (pixels) | `Height: integer` | `IMAGE img (Height: 150)` |
@@ -383,7 +383,7 @@ MDL uses explicit property declarations for pages:
 | `ColumnWidth` | `autoFill`, `autoFit`, `manual` | `autoFill` | `ColumnWidth: manual` |
 | `Size` | integer (px) | `1` | `Size: 200` |
 | `Visible` | expression string | `true` | `Visible: '$showColumn'` (page variable, not $currentObject) |
-| `DynamicCellClass` | expression string | (empty) | `DynamicCellClass: 'if(...) then ... else ...'` |
+| `DynamicCellClass` | expression string | (empty) | `DynamicCellClass: if(...) then ... else ...` |
 | `Tooltip` | text string | (empty) | `Tooltip: 'Price in USD'` |
 
 **Page Example:**

docs-site/src/language/alter-page.md

@@ -43,7 +43,7 @@ ALTER PAGE Module.EditPage {
 | `ButtonStyle` | Button visual style | `SET ButtonStyle = Danger ON btnDelete` |
 | `Class` | CSS class names | `SET Class = 'card p-3' ON cMain` |
 | `Style` | Inline CSS | `SET Style = 'margin: 8px;' ON cBox` |
-| `DynamicClasses` | Runtime-computed CSS classes | `SET DynamicClasses = 'if $currentObject/IsActive then ''is-active'' else ''''' ON cMain` |
+| `DynamicClasses` | Runtime-computed CSS classes | `SET DynamicClasses = if $currentObject/IsActive then 'is-active' else '' ON cMain` |
 | `Editable` | Editability mode | `SET Editable = ReadOnly ON txtEmail` |
 | `Visible` | Visibility expression | `SET Visible = '$showField' ON txtPhone` |
 | `Name` | Widget name | `SET Name = 'txtFullName' ON txtName` |

docs-site/src/language/widget-types.md

@@ -69,7 +69,7 @@ CONTAINER cCard (Class: 'card mx-spacing-top-large') {
 |----------|-------------|---------|
 | `Class` | CSS class names | `Class: 'card p-3'` |
 | `Style` | Inline CSS styles | `Style: 'padding: 16px;'` |
-| `DynamicClasses` | Runtime-computed CSS classes (expression; stacks on `Class`) | `DynamicClasses: 'if $currentObject/IsActive then ''is-active'' else '''''` |
+| `DynamicClasses` | Runtime-computed CSS classes (expression; stacks on `Class`) | `DynamicClasses: if $currentObject/IsActive then 'is-active' else ''` |
 | `DesignProperties` | Design property values | `DesignProperties: ['Spacing top': 'Large']` |
 
 ### CUSTOMCONTAINER
@@ -566,7 +566,7 @@ These properties are shared across many widget types:
 |----------|-------------|---------|
 | `Class` | CSS class names | `Class: 'card p-3'` |
 | `Style` | Inline CSS styles | `Style: 'margin-top: 8px;'` |
-| `DynamicClasses` | Runtime-computed CSS classes (expression; stacks on `Class`) | `DynamicClasses: 'if $currentObject/IsActive then ''is-active'' else '''''` |
+| `DynamicClasses` | Runtime-computed CSS classes (expression; stacks on `Class`) | `DynamicClasses: if $currentObject/IsActive then 'is-active' else ''` |
 | `DesignProperties` | Atlas design properties | `DesignProperties: ['Spacing top': 'Large', 'Full width': ON]` |
 | `Visible` | Visibility expression | `Visible: '$showSection'` |
 | `Editable` | Editability mode | `Editable: ReadOnly` |

docs-site/src/reference/page/create-page.md

@@ -190,7 +190,7 @@ These properties are available on most widget types:
 |----------|-------------|---------|
 | `Class` | CSS class names | `Class: 'card mx-spacing-top-large'` |
 | `Style` | Inline CSS | `Style: 'padding: 16px;'` |
-| `DynamicClasses` | Runtime-computed CSS classes (expression; stacks on `Class`) | `DynamicClasses: 'if $currentObject/IsActive then ''is-active'' else '''''` |
+| `DynamicClasses` | Runtime-computed CSS classes (expression; stacks on `Class`) | `DynamicClasses: if $currentObject/IsActive then 'is-active' else ''` |
 | `Editable` | Edit control | `Editable: NEVER` or `Editable: ALWAYS` |
 | `Visible` | Visibility expression | `Visible: '$showField'` |
 | `DesignProperties` | Atlas design properties | `DesignProperties: ['Spacing top': 'Large']` |

docs/01-project/MDL_QUICK_REFERENCE.md

@@ -1455,7 +1455,7 @@ MDL uses explicit property declarations for pages:
 | Association source ("data from context") | `datasource: $currentObject/Module.Assoc` | nested `dataview dvCust (datasource: $currentObject/Order_Customer)` shows the to-one referenced object; a list widget shows the to-many collection |
 | CSS class | `class: 'classes'` | `container c (class: 'card mx-spacing-top-large')` |
 | Inline style | `style: 'css'` | `container c (style: 'padding: 16px;')` |
-| Dynamic classes | `dynamicclasses: 'expr'` | `container c (dynamicclasses: 'if $currentObject/IsActive then ''is-active'' else ''''')` — runtime-computed classes; stacks on `class` |
+| Dynamic classes | `dynamicclasses: 'expr'` | `container c (dynamicclasses: if $currentObject/IsActive then 'is-active' else '')` — runtime-computed classes; stacks on `class` |
 | Design properties | `designproperties: [...]` | `container c (designproperties: ['Spacing top': 'Large', 'full width': on])` |
 | Width (pixels) | `width: integer` | `image img (width: 200)` |
 | Height (pixels) | `height: integer` | `image img (height: 150)` |
@@ -1521,7 +1521,7 @@ MDL uses explicit property declarations for pages:
 | `ColumnWidth` | `autofill`, `autoFit`, `manual` | `autofill` | `ColumnWidth: manual` |
 | `Size` | integer (px) | `1` | `Size: 200` |
 | `visible` | expression string | `true` | `visible: '$showColumn'` (page variable, not $currentObject) |
-| `DynamicCellClass` | expression string | (empty) | `DynamicCellClass: 'if(...) then ... else ...'` |
+| `DynamicCellClass` | expression string | (empty) | `DynamicCellClass: if(...) then ... else ...` |
 | `tooltip` | text string | (empty) | `tooltip: 'Price in USD'` |
 
 **Page Example:**

docs/11-proposals/PROPOSAL_first_class_expressions.md

@@ -232,6 +232,12 @@ proposals compose rather than compete.
    otherwise quote. Confirm this output variance is acceptable.
 
 4. **Pluggable expression properties are resolved by schema, not by name.**
+   **Decided 2026-09-25: (a)**, shipped in two steps. First the named
+   properties, `DynamicClasses` and a column's `DynamicCellClass`: written
+   as-is, a quoted value is a string (the Q5 rule), and the old quoted-text
+   spelling is refused as MDL-WIDGET33. Then the schema-driven extension to every
+   pluggable property whose kind is Expression.
+
    Slice 2 either (a) lets any generic property take a bare expression and
    rejects it at check time when the widget schema says the slot is not
    `expression`-typed, or (b) adds the bare form only for the named properties
@@ -376,6 +382,10 @@ quoted output with the bare form.
 
 **Slice 2 — expression family, widget slots.**
 
+*Named-property step done (2026-09-25):* `DynamicClasses` and `DynamicCellClass`
+take the expression as written through `create page`, `alter page … set` and
+`describe`. The table below is the schema-driven remainder.
+
 | File | Change |
 |---|---|
 | `mdl/grammar/domains/MDLPage.g4` | `widgetPropertyV3`: add `(IDENTIFIER \| keyword) COLON expression` **after** every existing generic branch, so `'text'`, numbers, booleans, qualified names and `[ … ]` keep their current parse and only what those reject (`if …`, `$v/Attr + …`, calls) reaches it. `make grammar`; watch for new ambiguity reports. |

mdl-examples/bug-tests/750-dynamicclasses-legacy-quoted-expression.fail.mdl

@@ -0,0 +1,16 @@
+-- mendixlabs/mxcli#750, PROPOSAL_first_class_expressions.md slice 2 (named
+-- properties): DynamicClasses and a datagrid column's DynamicCellClass hold a
+-- Mendix expression written as-is.
+--
+--   dynamicclasses: if $currentObject/Featured then 'is-featured' else ''
+--   dynamicclasses: 'is-featured'          -- the string: the class is-featured
+--
+-- The old spelling — the expression's text in quotes, with its own quotes
+-- doubled — still parses, and would now store that text as a class name. check
+-- and exec refuse it as MDL-WIDGET33 and name the unquoted expression.
+--
+-- This file must FAIL `mxcli check`.
+
+create page Legacy.P (title: 'P', layout: Atlas_Core.Atlas_Default) {
+  container c1 (dynamicclasses: 'if $currentObject/Featured then ''is-featured'' else ''''') { }
+}

mdl-examples/bug-tests/alter-page-lowercase-set-on-builtin.mdl

@@ -55,7 +55,7 @@ create or replace page MyFirstModule.P_LowerSet
 -- Every one of these used to hard-error "widget has no pluggable Object".
 alter page MyFirstModule.P_LowerSet {
   set class = 'fl-topbar' on topBar;
-  set dynamicclasses = 'if $currentObject/Name != '''' then ''is-named'' else '''''  on topBar;
+  set dynamicclasses = if $currentObject/Name != '' then 'is-named' else ''  on topBar;
   set class = 'fl-badge' on rowBadge;
   set caption = 'Shortcuts' on btnKeys;
 }

mdl-examples/bug-tests/bug10-dynamic-css-classes.mdl

@@ -39,7 +39,7 @@ create page BugTests.Bug10 (
         dynamictext t1 (
           content: 'hi',
           class: 'base',
-          dynamicclasses: 'if 1 = 1 then ''mod-a'' else ''mod-b'''
+          dynamicclasses: if 1 = 1 then 'mod-a' else 'mod-b'
         )
         -- 10a: DataGrid2 column DynamicCellClass must persist as an expression
         datagrid dg1 (
@@ -49,7 +49,7 @@ create page BugTests.Bug10 (
           column colStatus (
             Attribute: FullName,
             Caption: 'Name',
-            DynamicCellClass: 'if $currentObject/FullName = ''x'' then ''ea-ok'' else ''ea-draft'''
+            DynamicCellClass: if $currentObject/FullName = 'x' then 'ea-ok' else 'ea-draft'
           )
         }
       }

mdl-examples/bug-tests/widget-dynamicclasses.mdl

@@ -40,12 +40,12 @@ create or replace page MyFirstModule.P_DynClass
     dynamictext ovClass (
       Content: 'chip',
       Class: 'ss-chip',
-      DynamicClasses: 'if $currentObject/Name = ''Astute'' then ''ss-chip--astute'' else '''''
+      DynamicClasses: if $currentObject/Name = 'Astute' then 'ss-chip--astute' else ''
     )
     -- DynamicClasses on a container
     container ovBox (
       Class: 'ss-box',
-      DynamicClasses: 'if $currentObject/Name = '''' then ''ss-box--empty'' else '''''
+      DynamicClasses: if $currentObject/Name = '' then 'ss-box--empty' else ''
     ) {
       dynamictext boxLabel (content: 'inner')
     }
@@ -58,7 +58,7 @@ create or replace page MyFirstModule.P_DynClass
 -- hard error "widget has no pluggable Object" on core widgets).
 alter page MyFirstModule.P_DynClass {
   set Class = 'ss-later' on ovLater;
-  set DynamicClasses = 'if $currentObject/Name != '''' then ''ss-later--named'' else '''''  on ovLater;
+  set DynamicClasses = if $currentObject/Name != '' then 'ss-later--named' else ''  on ovLater;
 }
 
 describe page MyFirstModule.P_DynClass;