📍 NOTE
RubyGems (the GitHub org, not the website) suffered a hostile takeover in September 2025.
Ultimately 4 maintainers were hard removed and a reason has been given for only 1 of those, while 2 others resigned in protest.
It is a complicated story which is difficult to parse quickly.
Simply put - there was active policy for adding or removing maintainers/owners of rubygems and bundler, and those policies were not followed.
I'm adding notes like this to gems because I don't condone theft of repositories or gems from their rightful owners.
If a similar theft happened with my repos/gems, I'd hope some would stand up for me.
Disenfranchised former-maintainers have started gem.coop.
Once available I will publish there exclusively; unless RubyCentral makes amends with the community.
The "Technology for Humans: Joel Draper" podcast episode by reinteractive is the most cogent summary I'm aware of.
See here, here and here for more info on what comes next.
What I'm doing: A (WIP) proposal for bundler/gem scopes, and a (WIP) proposal for a federated gem server.

☯️ Markdown::Merge

if ci_badges.map(&:color).detect { it != "green"} ☝️ let me know, as I may have missed the discord notification.

---

if ci_badges.map(&:color).all? { it == "green"} 👇️ send money so I can do more of this. FLOSS maintenance is now my full-time job.

🌻 Synopsis

Markdown::Merge is a shared foundation for intelligent Markdown file merging. It provides base classes and utilities that parser-specific implementations use to merge Markdown documents by understanding their structure.

Important: This gem is not typically used directly. Instead, use one of the parser-specific implementations:

• commonmarker-merge - Uses Comrak (Rust) for parsing
• markly-merge - Uses libcmark-gfm (C) for parsing

Key Features

• Parser-Agnostic Base Classes: Provides SmartMergerBase, FileAnalysisBase, and other foundation components
• Structure-Aware: Understands headings, paragraphs, lists, code blocks, tables, and other block elements
• Freeze Block Support: Respects freeze markers (default: markdown-merge:freeze / markdown-merge:unfreeze) for template merge control - customizable to match your project's conventions
• Inner-Merge Code Blocks: Optionally merge fenced code blocks using language-specific mergers (Ruby → prism-merge, YAML → psych-merge, JSON → json-merge, TOML → toml-merge)
• Table Match Refiner: Fuzzy matching algorithm for tables with similar but not identical headers
• Full Provenance: Tracks origin of every node
• Customizable:
  • signature_generator - callable custom signature generators
  • preference - setting of :template, :destination, or a Hash for per-node-type preferences
  • add_template_only_nodes - setting to retain sections that do not exist in destination
  • freeze_token - customize freeze block markers (default: "markdown-merge")
  • inner_merge_code_blocks - enable language-aware code block merging
  • match_refiner - fuzzy matching for unmatched nodes (e.g., TableMatchRefiner)

Supported Node Types

Signatures computed by default for common Markdown block elements:

Node Type	Signature Format	Matching Behavior
Heading	[:heading, level, text]	Headings match by level and text content
Paragraph	[:paragraph, content_hash]	Paragraphs match by content hash
List	[:list, type, item_count]	Lists match by type (bullet/ordered) and item count
Code Block	[:code_block, language, content_hash]	Code blocks match by language and content
Block Quote	[:blockquote, content_hash]	Block quotes match by content hash
Table	[:table, row_count, header_hash]	Tables match by structure and header content
HTML Block	[:html, content_hash]	HTML blocks match by content hash
Thematic Break	[:hrule]	Horizontal rules always match
Footnote Definition	[:footnote_definition, label]	Footnotes match by label/name

The *-merge Gem Family

This gem is part of a family of gems that provide intelligent merging for various file formats:

Gem	Format	Parser	Description
ast-merge	Text	internal	Shared infrastructure for all *-merge gems
prism-merge	Ruby	Prism	Smart merge for Ruby source files
psych-merge	YAML	Psych	Smart merge for YAML files
json-merge	JSON	tree-sitter-json	Smart merge for JSON files
jsonc-merge	JSONC	tree-sitter-jsonc	⚠️ Proof of concept; Smart merge for JSON with Comments
bash-merge	Bash	tree-sitter-bash	Smart merge for Bash scripts
rbs-merge	RBS	RBS	Smart merge for Ruby type signatures
dotenv-merge	Dotenv	internal (dotenv)	Smart merge for .env files
toml-merge	TOML	tree-sitter-toml	Smart merge for TOML files
markdown-merge	Markdown	base classes	Shared foundation for Markdown mergers
markly-merge	Markdown	Markly	Smart merge for Markdown (CommonMark via libcmark-gfm)
commonmarker-merge	Markdown	Commonmarker	Smart merge for Markdown (CommonMark via comrak)

Example implementations for the gem templating use case:

Gem	Purpose	Description
kettle-dev	Gem Development	Gem templating tool using *-merge gems
kettle-jem	Gem Templating	Gem template library with smart merge support

💡 Info you can shake a stick at

Tokens to Remember
Works with JRuby
Works with Truffle Ruby
Works with MRI Ruby 3
Support & Community
Source
Documentation
Compliance
Style
Maintainer 🎖️
... 💖	🧊 🐙 🛖 🧪

Compatibility

Compatible with MRI Ruby 3.2.0+, and concordant releases of JRuby, and TruffleRuby.

🚚 Amazing test matrix was brought to you by	🔎 appraisal2 🔎 and the color 💚 green 💚
👟 Check it out!	✨ github.com/appraisal-rb/appraisal2 ✨

Federated DVCS

Find this repo on federated forges (Coming soon!)

Federated DVCS Repository	Status	Issues	PRs	Wiki	CI	Discussions
🧪 kettle-rb/markdown-merge on GitLab	The Truth	💚	💚	💚	🐭 Tiny Matrix	➖
🧊 kettle-rb/markdown-merge on CodeBerg	An Ethical Mirror (Donate)	💚	💚	➖	⭕️ No Matrix	➖
🐙 kettle-rb/markdown-merge on GitHub	Another Mirror	💚	💚	💚	💯 Full Matrix	💚
🎮️ Discord Server		Let's	talk	about	this	library!

Enterprise Support

Available as part of the Tidelift Subscription.

Need enterprise-level guarantees?

The maintainers of this and thousands of other packages are working with Tidelift to deliver commercial support and maintenance for the open source packages you use to build your applications. Save time, reduce risk, and improve code health, while paying the maintainers of the exact packages you use.

• 💡Subscribe for support guarantees covering all your FLOSS dependencies
• 💡Tidelift is part of Sonar
• 💡Tidelift pays maintainers to maintain the software you depend on!
  📊@Pointy Haired Boss: An enterprise support subscription is "never gonna let you down", and supports open source maintainers

Alternatively:

• 
• 
• 

✨ Installation

Install the gem and add to the application's Gemfile by executing:

bundle add markdown-merge

If bundler is not being used to manage dependencies, install the gem by executing:

gem install markdown-merge

🔒 Secure Installation

For Medium or High Security Installations

This gem is cryptographically signed, and has verifiable SHA-256 and SHA-512 checksums by stone_checksums. Be sure the gem you install hasn’t been tampered with by following the instructions below.

Add my public key (if you haven’t already, expires 2045-04-29) as a trusted certificate:

gem cert --add <(curl -Ls https://raw.github.com/galtzo-floss/certs/main/pboling.pem)

You only need to do that once. Then proceed to install with:

gem install markdown-merge -P HighSecurity

The HighSecurity trust profile will verify signed gems, and not allow the installation of unsigned dependencies.

If you want to up your security game full-time:

bundle config set --global trust-policy MediumSecurity

MediumSecurity instead of HighSecurity is necessary if not all the gems you use are signed.

NOTE: Be prepared to track down certs for signed gems and add them the same way you added mine.

⚙️ Configuration

This section documents configuration options available to parser-specific implementations. End users should refer to commonmarker-merge or markly-merge documentation for usage.

SmartMergerBase Configuration

The SmartMergerBase class accepts the following configuration options:

# Configuration options available to subclasses
merger = SomeParser::Merge::SmartMerger.new(
  template_content,
  dest_content,

  # Which version to prefer when nodes match but differ
  # :destination (default) - keep destination content (preserves customizations)
  # :template - use template content (applies updates)
  preference: :destination,

  # Whether to add template-only nodes to the result
  # false (default) - only include sections that exist in destination
  # true - include all template sections
  add_template_only_nodes: false,

  # Token for freeze block markers
  # Default: "markdown-merge"
  # Looks for: <!-- markdown-merge:freeze --> / <!-- markdown-merge:unfreeze -->
  freeze_token: "markdown-merge",

  # Enable inner-merge for fenced code blocks
  # false (default) - use standard conflict resolution for code blocks
  # true - merge code block contents using language-specific mergers
  # CodeBlockMerger instance - use custom CodeBlockMerger
  inner_merge_code_blocks: false,

  # Match refiner for fuzzy matching of unmatched nodes
  # nil (default) - exact matching only
  # TableMatchRefiner.new - enable fuzzy table matching
  match_refiner: nil,

  # Custom signature generator (optional)
  # Receives a node, returns a signature array or nil
  # Return the node itself to fall through to default signature
  signature_generator: nil,
)

Freeze Blocks

Freeze blocks protect sections from being modified during merges. They are marked with HTML comments that are invisible when the Markdown is rendered:

<!-- markdown-merge:freeze -->
## This Section Is Protected

Any content here will be preserved exactly as-is during merges.
The merge tool will not modify, replace, or remove this content.

<!-- markdown-merge:unfreeze -->

You can add an optional reason to document why a section is frozen:

<!-- markdown-merge:freeze Custom table - manually maintained -->
| Feature | Status |
|---------|--------|
| Custom  | ✅     |
<!-- markdown-merge:unfreeze -->

Inner-Merge Code Blocks

When enabled, fenced code blocks are merged using language-specific *-merge gems:

merger = SomeParser::Merge::SmartMerger.new(
  template,
  destination,
  inner_merge_code_blocks: true,
)

Supported languages and their mergers:

Language	Fence Info	Merger
Ruby	ruby, rb	prism-merge
YAML	yaml, yml	psych-merge
JSON	json	json-merge
TOML	toml	toml-merge

Example with a Ruby code block:

```ruby
# Template
class MyClass
  def new_method
    puts "from template"
  end
end
```

When merged with:

```ruby
# Destination
class MyClass
  def existing_method
    puts "custom"
  end
end
```

Result (with inner_merge_code_blocks: true):

```ruby
class MyClass
  def existing_method
    puts "custom"
  end

  def new_method
    puts "from template"
  end
end
```

Table Match Refiner

When tables don't match by exact signature, the TableMatchRefiner uses fuzzy matching to pair tables with similar structure:

refiner = Markdown::Merge::TableMatchRefiner.new(
  threshold: 0.5,  # Minimum similarity (0.0-1.0)
  algorithm_options: {
    weights: {
      header_match: 0.25,  # Header cell similarity
      first_column: 0.20,  # Row label similarity
      row_content: 0.25,   # Row content overlap
      total_cells: 0.15,   # Overall cell matching
      position: 0.15,      # Position distance
    },
  },
)

merger = SomeParser::Merge::SmartMerger.new(
  template,
  destination,
  match_refiner: refiner,
)

Debug Logging

Enable debug logging to see merge decisions:

export MARKDOWN_MERGE_DEBUG=1

🔧 Basic Usage

Note: This gem provides base classes for implementers. End users should use commonmarker-merge or markly-merge instead.

For End Users

Use a parser-specific implementation:

# Option 1: Using commonmarker-merge (Comrak/Rust)
require "commonmarker/merge"

template = File.read("template.md")
destination = File.read("destination.md")

merger = Commonmarker::Merge::SmartMerger.new(template, destination)
result = merger.merge

File.write("merged.md", result.content)

# Option 2: Using markly-merge (libcmark-gfm/C)
require "markly/merge"

template = File.read("template.md")
destination = File.read("destination.md")

merger = Markly::Merge::SmartMerger.new(template, destination)
result = merger.merge

File.write("merged.md", result.to_markdown)

For Implementers

Creating a new parser-specific implementation:

require "markdown/merge"

module MyParser
  module Merge
    class FileAnalysis < Markdown::Merge::FileAnalysisBase
      def parse_document(source)
        # Parse source and return root document node
        MyParser.parse(source)
      end

      def next_sibling(node)
        # Return the next sibling of a node
        node.next_sibling
      end

      def compute_parser_signature(node)
        # Compute signature for parser-specific nodes
        # Or call super for default implementation
        super
      end
    end

    class SmartMerger < Markdown::Merge::SmartMergerBase
      def create_file_analysis(content, **options)
        FileAnalysis.new(content, **options)
      end

      def node_to_source(node, analysis)
        case node
        when Markdown::Merge::FreezeNode
          node.full_text
        else
          # Convert node back to source text
          node.to_markdown
        end
      end
    end
  end
end

Freeze Block Protection

Both implementations support freeze blocks for protecting customized sections:

# My Project

## Installation

<!-- markdown-merge:freeze Custom install instructions -->
This installation section has been customized and will be preserved
during template merges, regardless of what the template contains.
<!-- markdown-merge:unfreeze -->

## Usage

Standard usage section - can be updated from template.

Content between freeze markers is always preserved from the destination file, even when the template has different content for that section.

🦷 FLOSS Funding

While kettle-rb tools are free software and will always be, the project would benefit immensely from some funding. Raising a monthly budget of... "dollars" would make the project more sustainable.

We welcome both individual and corporate sponsors! We also offer a wide array of funding channels to account for your preferences (although currently Open Collective is our preferred funding platform).

If you're working in a company that's making significant use of kettle-rb tools we'd appreciate it if you suggest to your company to become a kettle-rb sponsor.

You can support the development of kettle-rb tools via GitHub Sponsors, Liberapay, PayPal, Open Collective and Tidelift.

📍 NOTE
If doing a sponsorship in the form of donation is problematic for your company from an accounting standpoint, we'd recommend the use of Tidelift, where you can get a support-like subscription instead.

Open Collective for Individuals

Support us with a monthly donation and help us continue our activities. [Become a backer]

NOTE: kettle-readme-backers updates this list every day, automatically.

No backers yet. Be the first!

Open Collective for Organizations

Become a sponsor and get your logo on our README on GitHub with a link to your site. [Become a sponsor]

NOTE: kettle-readme-backers updates this list every day, automatically.

No sponsors yet. Be the first!

Another way to support open-source

I’m driven by a passion to foster a thriving open-source community – a space where people can tackle complex problems, no matter how small. Revitalizing libraries that have fallen into disrepair, and building new libraries focused on solving real-world challenges, are my passions. I was recently affected by layoffs, and the tech jobs market is unwelcoming. I’m reaching out here because your support would significantly aid my efforts to provide for my family, and my farm (11 🐔 chickens, 2 🐶 dogs, 3 🐰 rabbits, 8 🐈‍ cats).

If you work at a company that uses my work, please encourage them to support me as a corporate sponsor. My work on gems you use might show up in bundle fund.

I’m developing a new library, floss_funding, designed to empower open-source developers like myself to get paid for the work we do, in a sustainable way. Please give it a look.

Floss-Funding.dev: 👉️ No network calls. 👉️ No tracking. 👉️ No oversight. 👉️ Minimal crypto hashing. 💡 Easily disabled nags

🔐 Security

See SECURITY.md.

🤝 Contributing

If you need some ideas of where to help, you could work on adding more code coverage, or if it is already 💯 (see below) check reek, issues, or PRs, or use the gem and think about how it could be better.

We so if you make changes, remember to update it.

See CONTRIBUTING.md for more detailed instructions.

🚀 Release Instructions

See CONTRIBUTING.md.

Code Coverage

🪇 Code of Conduct

Everyone interacting with this project's codebases, issue trackers, chat rooms and mailing lists agrees to follow the .

🌈 Contributors

Made with contributors-img.

Also see GitLab Contributors: https://gitlab.com/kettle-rb/markdown-merge/-/graphs/main

⭐️ Star History

📌 Versioning

This Library adheres to . Violations of this scheme should be reported as bugs. Specifically, if a minor or patch version is released that breaks backward compatibility, a new version should be immediately released that restores compatibility. Breaking changes to the public API will only be introduced with new major versions.

dropping support for a platform is both obviously and objectively a breaking change
—Jordan Harband (@ljharb, maintainer of SemVer) in SemVer issue 716

I understand that policy doesn't work universally ("exceptions to every rule!"), but it is the policy here. As such, in many cases it is good to specify a dependency on this library using the Pessimistic Version Constraint with two digits of precision.

For example:

spec.add_dependency("markdown-merge", "~> 1.0")

📌 Is "Platform Support" part of the public API? More details inside.

SemVer should, IMO, but doesn't explicitly, say that dropping support for specific Platforms is a breaking change to an API, and for that reason the bike shedding is endless.

To get a better understanding of how SemVer is intended to work over a project's lifetime, read this article from the creator of SemVer:

• "Major Version Numbers are Not Sacred"

See CHANGELOG.md for a list of releases.

📄 License

The gem is available as open source under the terms of the MIT License . See LICENSE.txt for the official Copyright Notice.

© Copyright

• Copyright (c) 2023, 2025 Peter H. Boling, of Galtzo.com , and markdown-merge contributors.

🤑 A request for help

Maintainers have teeth and need to pay their dentists. After getting laid off in an RIF in March, and encountering difficulty finding a new one, I began spending most of my time building open source tools. I'm hoping to be able to pay for my kids' health insurance this month, so if you value the work I am doing, I need your support. Please consider sponsoring me or the project.

To join the community or get help 👇️ Join the Discord.

To say "thanks!" ☝️ Join the Discord or 👇️ send money.

💌 💌 💌

Please give the project a star ⭐ ♥.

Thanks for RTFM. ☺️