Add list item attribute support (#5)

List items can now have attributes on the following line at content indent:

```djot
- item 1
  {.highlight #id1}
- item 2
  {data-value="test"}
```

Renders as:
```html
<li class="highlight" id="id1">item 1</li>
<li data-value="test">item 2</li>
```

Works with:
- Unordered lists
- Ordered lists
- Task lists

Related: jgm/djot#262

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude <noreply@anthropic.com>

Author: dereuromark

src/Parser/BlockParser.php

@@ -712,6 +712,41 @@ protected function processAttributeEscapes(string $value): string
         return preg_replace('/\\\\(.)/', '$1', $value) ?? $value;
     }
 
+    /**
+     * Parse attribute string and return as array (without affecting pendingAttributes)
+     *
+     * @return array<string, string>
+     */
+    protected function parseAttributeStringToArray(string $attrStr): array
+    {
+        $attributes = [];
+
+        // Parse .class
+        if (preg_match_all('/\.([^\s.#=}]+)/', $attrStr, $classMatches)) {
+            $attributes['class'] = implode(' ', $classMatches[1]);
+        }
+
+        // Parse #id
+        if (preg_match('/#([^\s.#=}]+)/', $attrStr, $idMatch)) {
+            $attributes['id'] = $idMatch[1];
+        }
+
+        // Parse key="double quoted value", key='single quoted value', or key=unquoted
+        if (preg_match_all('/([a-zA-Z_][a-zA-Z0-9_-]*)="((?:[^"\\\\]|\\\\.)*)"|([a-zA-Z_][a-zA-Z0-9_-]*)=\'((?:[^\'\\\\]|\\\\.)*)\'|([a-zA-Z_][a-zA-Z0-9_-]*)=([^\s}"\']+)/', $attrStr, $kvMatches, PREG_SET_ORDER)) {
+            foreach ($kvMatches as $match) {
+                if (($match[1] ?? '') !== '') {
+                    $attributes[$match[1]] = $this->processAttributeEscapes($match[2] ?? '');
+                } elseif (($match[3] ?? '') !== '') {
+                    $attributes[$match[3]] = $this->processAttributeEscapes($match[4] ?? '');
+                } elseif (($match[5] ?? '') !== '') {
+                    $attributes[$match[5]] = $match[6] ?? '';
+                }
+            }
+        }
+
+        return $attributes;
+    }
+
     /**
      * Apply pending attributes to a node and clear them
      */
@@ -1508,6 +1543,15 @@ protected function tryParseList(Node $parent, array $lines, int $start): ?int
                     }
                 }
 
+                // Check for list item attributes (must be at content indent, be a standalone attribute block)
+                if (
+                    $nextIndent >= $contentIndent &&
+                    preg_match('/^\{([^{}]+)\}\s*$/', $nextTrimmed, $attrMatch)
+                ) {
+                    // This is a list item attribute line - don't add to content
+                    break;
+                }
+
                 // Content at content indent or more is continuation (even if it looks like a list marker)
                 // In djot, "  - b" after "- a" (no blank line) is literal text, not a nested list
                 if ($nextIndent >= $contentIndent) {
@@ -1521,6 +1565,21 @@ protected function tryParseList(Node $parent, array $lines, int $start): ?int
                 $i++;
             }
 
+            // Check for list item attributes on the next line
+            $itemAttributes = [];
+            if ($i < $count) {
+                $potentialAttrLine = $lines[$i];
+                $trimmedAttrLine = ltrim($potentialAttrLine);
+                // Check if it's an attribute block at content indent level
+                if (
+                    preg_match('/^\{([^{}]+)\}\s*$/', $trimmedAttrLine, $attrMatch) &&
+                    $this->getLeadingSpaces($potentialAttrLine) >= $contentIndent
+                ) {
+                    $itemAttributes = $this->parseAttributeStringToArray($attrMatch[1]);
+                    $i++;
+                }
+            }
+
             // For tight lists with continuation lines, parse as plain text
             // This prevents "-like" lines from being parsed as nested lists
             if ($hasNonMarkerContinuation) {
@@ -1530,6 +1589,13 @@ protected function tryParseList(Node $parent, array $lines, int $start): ?int
             } else {
                 $this->parseBlocks($listItem, $itemLines, 0);
             }
+
+            // Apply attributes to list item
+            if ($itemAttributes !== []) {
+                foreach ($itemAttributes as $key => $value) {
+                    $listItem->setAttribute($key, $value);
+                }
+            }
             $list->appendChild($listItem);
         }
 

tests/TestCase/DjotConverterTest.php

@@ -758,6 +758,54 @@ public function testOrderedListStartNumber(): void
         $this->assertStringContainsString('First', $result);
     }
 
+    public function testListItemAttributes(): void
+    {
+        $djot = "- item 1\n  {.highlight}\n- item 2";
+
+        $result = $this->converter->convert($djot);
+
+        $this->assertStringContainsString('<li class="highlight">', $result);
+        $this->assertStringContainsString('item 1', $result);
+        $this->assertStringContainsString('item 2', $result);
+    }
+
+    public function testListItemAttributesWithId(): void
+    {
+        $djot = "- first item\n  {#first .important}\n- second item";
+
+        $result = $this->converter->convert($djot);
+
+        $this->assertStringContainsString('<li id="first" class="important">', $result);
+    }
+
+    public function testListItemAttributesWithCustomAttribute(): void
+    {
+        $djot = "- item\n  {data-value=\"test\"}";
+
+        $result = $this->converter->convert($djot);
+
+        $this->assertStringContainsString('data-value="test"', $result);
+    }
+
+    public function testOrderedListItemAttributes(): void
+    {
+        $djot = "1. first\n   {.step-one}\n2. second";
+
+        $result = $this->converter->convert($djot);
+
+        $this->assertStringContainsString('<li class="step-one">', $result);
+    }
+
+    public function testTaskListItemAttributes(): void
+    {
+        $djot = "- [x] done\n  {.completed}\n- [ ] pending";
+
+        $result = $this->converter->convert($djot);
+
+        $this->assertStringContainsString('<li class="completed">', $result);
+        $this->assertStringContainsString('checked=""', $result);
+    }
+
     public function testRomanNumeralList(): void
     {
         // x. is parsed as Roman numeral 10