Add pre tag support to paste HTML subset tool

[simonw]

Summary

• allow the sanitizer to retain <pre> tags and surface them in the supported elements list
• update the formatter to preserve whitespace inside preformatted blocks
• document that preformatted blocks are now supported by the tool

Testing

• no automated tests were run (not available)

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https://chatgpt.com/codex/tasks/task_e_68e0182480d883268e0ecc306f4bf163

[claude]

Claude finished @simonw's task —— View job

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PR Review: Add pre tag support to paste HTML subset tool

Review Todo List:

• Read repository guidelines (CLAUDE.md)
• Review modified files and understand changes
• Analyze code quality and best practices
• Check for potential bugs or issues
• Evaluate performance considerations
• Assess security concerns
• Review test coverage and documentation
• Provide comprehensive feedback

Summary

This PR successfully adds <pre> tag support to the HTML sanitizer tool with proper whitespace preservation. The implementation is solid and addresses the stated goals well.

✅ Strengths

Code Quality:

• Clean, readable implementation that follows existing patterns
• Good separation of concerns with the preStack mechanism
• Proper whitespace preservation using rawPart vs part in formatHtml() at line 280
• Consistent code style with the rest of the file

Implementation Details:

• Correctly adds 'pre' to allowedTags array at line 160
• Stack-based tracking of <pre> elements in formatHtml() prevents nested indentation issues
• Uses regex /^<pre\b/i and /^<\/pre\b/i for robust tag detection (lines 269, 256)
• Documentation updated to mention "preformatted blocks"

🔍 Minor Issues & Suggestions

Performance Considerations:

• The formatHtml() function processes HTML character-by-character which could be slow for very large content, but this is acceptable for the intended use case of pasting clipboard content

Code Robustness:

1. Edge case handling: The preStack implementation looks solid, but consider what happens with malformed HTML like <pre><pre></pre> - the current implementation handles this gracefully by popping only one item from the stack

2. Regex specificity: The regex patterns are good - using \b word boundaries prevents false matches on tags like <prepare>

Documentation:

• The change from "Code snippets" to "Inline code snippets" for <code> is a nice clarification that distinguishes it from <pre> blocks

🔒 Security Assessment

No security concerns identified:

• The <pre> tag is safe as it only affects text formatting
• No new attributes are being preserved (following the existing pattern of only allowing href for links)
• The sanitization logic remains robust

🧪 Test Coverage

Current state: As noted in the PR description, no automated tests were run (not available).

Recommendation: While not blocking for this PR, consider adding basic test cases for:

• Whitespace preservation inside <pre> blocks
• Nested elements handling within <pre>
• Malformed <pre> tags

✅ Overall Assessment

This is a well-implemented feature that cleanly adds <pre> tag support while maintaining code quality and security. The whitespace preservation logic is particularly well done. The changes are minimal, focused, and align perfectly with the stated goals.

Recommendation: Approve - This PR is ready to merge.

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[cloudflare-workers-and-pages]

Deploying tools with    Cloudflare Pages

Latest commit:	c33a5cf
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Preview URL:	https://374edba8.tools-b1q.pages.dev
Branch Preview URL:	https://codex-add-pre-support-to-pas.tools-b1q.pages.dev

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[claude]

Claude finished @simonw's task —— View job

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PR Review: Add pre tag support to paste HTML subset tool

Review Todo List:

• Read repository guidelines (CLAUDE.md) - No CLAUDE.md file found
• Review modified files and understand changes
• Analyze code quality and best practices
• Check for potential bugs or issues
• Evaluate performance considerations
• Assess security concerns
• Review test coverage and documentation
• Provide comprehensive feedback

Summary

This PR successfully adds <pre> tag support to the HTML sanitization tool with proper whitespace preservation during formatting. The implementation is solid and follows existing patterns in the codebase.

✅ Positive Aspects

Clean Implementation

• <pre> tag correctly added to allowedTags array (paste-html-subset.html:160)
• Updated documentation in supported elements list (paste-html-subset.html:119)
• Consistent with existing code patterns and style

Smart Whitespace Handling

• Proper preformatted block detection using preStack array (paste-html-subset.html:243)
• Preserves original content in <pre> blocks: const content = preStack.length > 0 ? rawPart : part; (paste-html-subset.html:280)
• Prevents trimming of whitespace inside preformatted content

Robust Formatting Logic

• Stack-based tracking handles nested elements correctly
• Regex patterns properly match opening/closing pre tags (paste-html-subset.html:256,269)
• Maintains indentation integrity outside pre blocks

🔍 Code Quality Assessment

Security: ✅ Excellent

• No XSS vulnerabilities introduced
• <pre> tag sanitization follows same safe patterns as other elements
• No attribute copying for <pre> tags (only href for links is preserved)

Performance: ✅ Good

• Minimal overhead from pre-tag handling
• Stack operations are O(1)
• No significant performance impact on existing functionality

Maintainability: ✅ Very Good

• Code is clear and well-structured
• Consistent naming conventions (preStack, descriptive regex patterns)
• Changes are minimal and focused

🧪 Testing Considerations

Missing Test Coverage

• No automated tests exist for this functionality (as noted in PR description)
• Consider adding tests for:
  • Basic <pre> tag preservation
  • Whitespace preservation inside pre blocks
  • Nested pre handling edge cases
  • Mixed content with pre and other elements

Manual Testing Suggestions

<pre>function example() {
    console.log("whitespace preserved");
}</pre>

<pre>
Multi-line
  with indentation
    preserved
</pre>

🐛 Potential Issues

Minor Edge Case (paste-html-subset.html:250)

if (!part && preStack.length === 0) continue;

Empty parts are skipped outside pre blocks but processed inside them. This is correct behavior but could benefit from a code comment explaining the logic.

Documentation Removal
The deletion of paste-html-subset.docs.md removes tool documentation. Consider:

• Was this intentional cleanup?
• Is documentation maintained elsewhere?
• Should usage examples be preserved?

📝 Recommendations

1. Add inline comment explaining preStack whitespace preservation logic
2. Consider test coverage for future maintainability
3. Verify documentation strategy - ensure tool description exists elsewhere if needed

🎯 Overall Assessment

This is a high-quality implementation that successfully adds pre-tag support while maintaining code safety and existing functionality. The changes are minimal, focused, and follow good practices.

Approval Recommendation: ✅ Approve - Ready to merge pending documentation verification.

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[simonw]

I tested this on https://374edba8.tools-b1q.pages.dev/paste-html-subset and it didn't work correctly, so I am abandoning it.