feat(html): add placeholder helper

Co-Authored-By: Virgil <virgil@lethean.io>

docs/architecture.md

@@ -54,6 +54,7 @@ Accessibility-oriented helpers are also provided for common attribute patterns:
 - `Dir(node, direction)`
 - `Alt(node, text)`
 - `Title(node, text)`
+- `Placeholder(node, text)`
 - `Class(node, classes...)`
 - `AriaHidden(node, hidden)`
 - `AriaExpanded(node, expanded)`

docs/index.md

@@ -39,7 +39,7 @@ This builds a Header-Content-Footer layout with semantic HTML elements (`<header
 
 | Path | Purpose |
 |------|---------|
-| `node.go` | `Node` interface and all node types: `El`, `Text`, `Raw`, `If`, `Unless`, `Each`, `EachSeq`, `Switch`, `Entitled`, plus `AriaLabel`, `AriaControls`, `AriaHasPopup`, `AriaOwns`, `AriaKeyShortcuts`, `Alt`/`AltText`, `Title`, `AriaBusy`, `AriaLive`, `AriaAtomic`, `AriaDescription`, `AriaDetails`, `AriaErrorMessage`, `AriaRoleDescription`, `AriaDisabled`, `AriaModal`, `AriaChecked`, `AriaInvalid`, `AriaRequired`, `AriaPressed`, `AriaSelected`, `Hidden`, `Disabled`, `Checked`, `Required`, `ReadOnly`, `Selected`, `TabIndex`, and `AutoFocus` helpers |
+| `node.go` | `Node` interface and all node types: `El`, `Text`, `Raw`, `If`, `Unless`, `Each`, `EachSeq`, `Switch`, `Entitled`, plus `AriaLabel`, `AriaControls`, `AriaHasPopup`, `AriaOwns`, `AriaKeyShortcuts`, `Alt`/`AltText`, `Title`, `Placeholder`, `AriaBusy`, `AriaLive`, `AriaAtomic`, `AriaDescription`, `AriaDetails`, `AriaErrorMessage`, `AriaRoleDescription`, `AriaDisabled`, `AriaModal`, `AriaChecked`, `AriaInvalid`, `AriaRequired`, `AriaPressed`, `AriaSelected`, `Hidden`, `Disabled`, `Checked`, `Required`, `ReadOnly`, `Selected`, `TabIndex`, and `AutoFocus` helpers |
 | `layout.go` | HLCRF compositor with semantic HTML elements and ARIA roles |
 | `responsive.go` | Multi-variant breakpoint wrapper (`data-variant` containers, CSS scoping helpers) |
 | `context.go` | Rendering context: identity, locale, entitlements, i18n service |
@@ -52,7 +52,7 @@ This builds a Header-Content-Footer layout with semantic HTML elements (`<header
 
 ## Key Concepts
 
-**Node tree** -- All renderable units implement `Node`, a single-method interface: `Render(ctx *Context) string`. The library composes nodes into trees using `El()` for elements, `Text()` for translated text, and control-flow constructors (`If`, `Unless`, `Each`, `Switch`, `Entitled`), plus accessibility and visibility helpers such as `AriaLabel()`, `AriaControls()`, `AriaHasPopup()`, `AriaOwns()`, `AriaKeyShortcuts()`, `AriaCurrent()`, `AriaBusy()`, `AriaLive()`, `AriaAtomic()`, `AriaDescription()`, `AriaDetails()`, `AriaErrorMessage()`, `AriaRoleDescription()`, `AriaHidden()`, `Hidden()`, `AriaDisabled()`, `AriaModal()`, `AriaChecked()`, `AriaInvalid()`, `AriaRequired()`, `AriaReadOnly()`, `Disabled()`, `Checked()`, `Required()`, `ReadOnly()`, `Selected()`, `TabIndex()`, and the common HTML attribute helpers `Alt()`, `AltText()`, `Title()`, `ID()`, `For()`, `Class()`, and `AutoFocus()`.
+**Node tree** -- All renderable units implement `Node`, a single-method interface: `Render(ctx *Context) string`. The library composes nodes into trees using `El()` for elements, `Text()` for translated text, and control-flow constructors (`If`, `Unless`, `Each`, `Switch`, `Entitled`), plus accessibility and visibility helpers such as `AriaLabel()`, `AriaControls()`, `AriaHasPopup()`, `AriaOwns()`, `AriaKeyShortcuts()`, `AriaCurrent()`, `AriaBusy()`, `AriaLive()`, `AriaAtomic()`, `AriaDescription()`, `AriaDetails()`, `AriaErrorMessage()`, `AriaRoleDescription()`, `AriaHidden()`, `Hidden()`, `AriaDisabled()`, `AriaModal()`, `AriaChecked()`, `AriaInvalid()`, `AriaRequired()`, `AriaReadOnly()`, `Disabled()`, `Checked()`, `Required()`, `ReadOnly()`, `Selected()`, `TabIndex()`, and the common HTML attribute helpers `Alt()`, `AltText()`, `Title()`, `Placeholder()`, `ID()`, `For()`, `Class()`, and `AutoFocus()`.
 
 **HLCRF Layout** -- A five-slot compositor that maps to semantic HTML: `<header>` (H), `<aside>` (L/R), `<main>` (C), `<footer>` (F). The variant string controls which slots render: `"HLCRF"` for all five, `"HCF"` for three, `"C"` for content only. Layouts nest: placing a `Layout` inside another layout's slot produces hierarchical `data-block` paths like `L-0-C-0`.
 

node.go

@@ -406,6 +406,16 @@ func Title(n Node, text string) Node {
 	return n
 }
 
+// node.go: Placeholder sets the placeholder attribute on an element node.
+// Example: Placeholder(El("input"), "Search by keyword").
+// An empty value leaves the node unchanged so callers can opt out cleanly.
+func Placeholder(n Node, text string) Node {
+	if value := trimmedNonEmpty(text); value != "" {
+		return Attr(n, "placeholder", value)
+	}
+	return n
+}
+
 // node.go: AltText is a compatibility alias for Alt.
 // Example: AltText(El("img"), "Product screenshot").
 // Prefer Alt for new call sites so the canonical image helper stays predictable.

node_test.go

@@ -663,6 +663,26 @@ func TestTitleHelper_IgnoresWhitespace(t *testing.T) {
 	}
 }
 
+func TestPlaceholderHelper(t *testing.T) {
+	ctx := NewContext()
+	node := Placeholder(El("input"), "Search by keyword")
+	got := node.Render(ctx)
+	want := `<input placeholder="Search by keyword">`
+	if got != want {
+		t.Errorf("Placeholder() = %q, want %q", got, want)
+	}
+}
+
+func TestPlaceholderHelper_IgnoresWhitespace(t *testing.T) {
+	ctx := NewContext()
+	node := Placeholder(El("input"), " \t ")
+	got := node.Render(ctx)
+	want := `<input>`
+	if got != want {
+		t.Errorf("Placeholder() with whitespace = %q, want %q", got, want)
+	}
+}
+
 func TestAltTextHelper(t *testing.T) {
 	ctx := NewContext()
 	node := AltText(El("img"), `A "quoted" caption`)