Add Folder Markdown format support

.gitignore

@@ -1,5 +1,228 @@
-*.egg-info
+# ** .gitignore for mu **
+
 TODO
 /dist
 
 /examples/olx.tar.gz
+/examples_output
+muenv
+.DS_Store
+
+# ** .gitignore for python **
+
+# Byte-compiled / optimized / DLL files
+__pycache__/
+*.py[codz]
+*$py.class
+
+# C extensions
+*.so
+
+# Distribution / packaging
+.Python
+build/
+develop-eggs/
+dist/
+downloads/
+eggs/
+.eggs/
+lib/
+lib64/
+parts/
+sdist/
+var/
+wheels/
+share/python-wheels/
+*.egg-info/
+.installed.cfg
+*.egg
+MANIFEST
+
+# PyInstaller
+#   Usually these files are written by a python script from a template
+#   before PyInstaller builds the exe, so as to inject date/other infos into it.
+*.manifest
+*.spec
+
+# Installer logs
+pip-log.txt
+pip-delete-this-directory.txt
+
+# Unit test / coverage reports
+htmlcov/
+.tox/
+.nox/
+.coverage
+.coverage.*
+.cache
+nosetests.xml
+coverage.xml
+*.cover
+*.py.cover
+.hypothesis/
+.pytest_cache/
+cover/
+
+# Translations
+*.mo
+*.pot
+
+# Django stuff:
+*.log
+local_settings.py
+db.sqlite3
+db.sqlite3-journal
+
+# Flask stuff:
+instance/
+.webassets-cache
+
+# Scrapy stuff:
+.scrapy
+
+# Sphinx documentation
+docs/_build/
+
+# PyBuilder
+.pybuilder/
+target/
+
+# Jupyter Notebook
+.ipynb_checkpoints
+
+# IPython
+profile_default/
+ipython_config.py
+
+# pyenv
+#   For a library or package, you might want to ignore these files since the code is
+#   intended to run in multiple environments; otherwise, check them in:
+# .python-version
+
+# pipenv
+#   According to pypa/pipenv#598, it is recommended to include Pipfile.lock in version control.
+#   However, in case of collaboration, if having platform-specific dependencies or dependencies
+#   having no cross-platform support, pipenv may install dependencies that don't work, or not
+#   install all needed dependencies.
+# Pipfile.lock
+
+# UV
+#   Similar to Pipfile.lock, it is generally recommended to include uv.lock in version control.
+#   This is especially recommended for binary packages to ensure reproducibility, and is more
+#   commonly ignored for libraries.
+# uv.lock
+
+# poetry
+#   Similar to Pipfile.lock, it is generally recommended to include poetry.lock in version control.
+#   This is especially recommended for binary packages to ensure reproducibility, and is more
+#   commonly ignored for libraries.
+#   https://python-poetry.org/docs/basic-usage/#commit-your-poetrylock-file-to-version-control
+# poetry.lock
+# poetry.toml
+
+# pdm
+#   Similar to Pipfile.lock, it is generally recommended to include pdm.lock in version control.
+#   pdm recommends including project-wide configuration in pdm.toml, but excluding .pdm-python.
+#   https://pdm-project.org/en/latest/usage/project/#working-with-version-control
+# pdm.lock
+# pdm.toml
+.pdm-python
+.pdm-build/
+
+# pixi
+#   Similar to Pipfile.lock, it is generally recommended to include pixi.lock in version control.
+# pixi.lock
+#   Pixi creates a virtual environment in the .pixi directory, just like venv module creates one
+#   in the .venv directory. It is recommended not to include this directory in version control.
+.pixi
+
+# PEP 582; used by e.g. github.com/David-OConnor/pyflow and github.com/pdm-project/pdm
+__pypackages__/
+
+# Celery stuff
+celerybeat-schedule
+celerybeat.pid
+
+# Redis
+*.rdb
+*.aof
+*.pid
+
+# RabbitMQ
+mnesia/
+rabbitmq/
+rabbitmq-data/
+
+# ActiveMQ
+activemq-data/
+
+# SageMath parsed files
+*.sage.py
+
+# Environments
+.env
+.envrc
+.venv
+env/
+venv/
+ENV/
+env.bak/
+venv.bak/
+
+# Spyder project settings
+.spyderproject
+.spyproject
+
+# Rope project settings
+.ropeproject
+
+# mkdocs documentation
+/site
+
+# mypy
+.mypy_cache/
+.dmypy.json
+dmypy.json
+
+# Pyre type checker
+.pyre/
+
+# pytype static type analyzer
+.pytype/
+
+# Cython debug symbols
+cython_debug/
+
+# PyCharm
+#   JetBrains specific template is maintained in a separate JetBrains.gitignore that can
+#   be found at https://github.com/github/gitignore/blob/main/Global/JetBrains.gitignore
+#   and can be added to the global gitignore or merged into this file.  For a more nuclear
+#   option (not recommended) you can uncomment the following to ignore the entire idea folder.
+# .idea/
+
+# Abstra
+#   Abstra is an AI-powered process automation framework.
+#   Ignore directories containing user credentials, local state, and settings.
+#   Learn more at https://abstra.io/docs
+.abstra/
+
+# Visual Studio Code
+#   Visual Studio Code specific template is maintained in a separate VisualStudioCode.gitignore 
+#   that can be found at https://github.com/github/gitignore/blob/main/Global/VisualStudioCode.gitignore
+#   and can be added to the global gitignore or merged into this file. However, if you prefer, 
+#   you could uncomment the following to ignore the entire vscode folder
+# .vscode/
+
+# Ruff stuff:
+.ruff_cache/
+
+# PyPI configuration file
+.pypirc
+
+# Marimo
+marimo/_static/
+marimo/_lsp/
+__marimo__/
+
+# Streamlit
+.streamlit/secrets.toml

README.md

@@ -4,16 +4,45 @@ Mu is for authors of online courses. It allows you to cross-compile courses from
 
 Supported formats:
 
-- [Markdown](https://daringfireball.net/projects/markdown/): with [Pandoc-flavoured](https://garrettgman.github.io/rmarkdown/authoring_pandoc_markdown.html) header attributes.
+- [Markdown](https://daringfireball.net/projects/markdown/): single file with [Pandoc-flavoured](https://garrettgman.github.io/rmarkdown/authoring_pandoc_markdown.html) header attributes.
+- [Folder Markdown](#folder-markdown): organized folder structure with multiple Markdown files.
 - HTML 5
 - Open Learning XML ([OLX](https://docs.openedx.org/en/latest/educators/navigation/olx.html)) from [Open edX](https://openedx.org).
 
-Check out the [course.md](https://github.com/overhangio/mu/blob/main/examples/course.md) file to see what an actual course in Markdown format looks like.
+Check out the [course.md](https://github.com/overhangio/mu/blob/main/examples/course.md) file to see what an actual course in single-file Markdown format looks like.
 
 ## Installation
 
+### Using PyPI (latest stable release)
+
     pip install mu-courses
 
+### Using the development version from source
+
+Since the PyPI version may not include the latest features and fixes, you can install directly from the repository:
+
+1. Clone the repository:
+    ```bash
+    git clone https://github.com/overhangio/mu.git
+    cd mu
+    ```
+
+2. Create a virtual environment:
+    ```bash
+    python -m venv venv
+    source venv/bin/activate  # On Windows: venv\Scripts\activate
+    ```
+
+3. Install in editable mode with development dependencies:
+    ```bash
+    pip install -e .
+    ```
+
+Alternatively, if you only want the latest features without development tools:
+    ```bash
+    pip install -e .
+    ```
+
 Conversion from and to Markdown is handled with the help of [Pandoc](https://pandoc.org/). Thus, a recent version of Pandoc is required when working with Markdown documents. See the corresponding [installation instructions](https://pandoc.org/installing.html).
 
 ## Usage
@@ -28,6 +57,78 @@ Conversion from and to Markdown is handled with the help of [Pandoc](https://pan
 
 When writing Markdown files, the generated documents will include non-standard (but widely recognized) [header identifiers](https://garrettgman.github.io/rmarkdown/authoring_pandoc_markdown.html#header-identifiers) to store the course unit attributes.
 
+### Folder Markdown
+
+For large courses, you can organize your content across multiple Markdown files in a folder structure instead of a single file. This is useful for team collaboration and better file organization.
+
+**Folder structure:**
+
+```
+course_folder/
+├── index.md                     # Course metadata and description
+├── chapter1/
+│   ├── index.md                 # Chapter metadata
+│   ├── sequential1/
+│   │   ├── index.md             # Sequential metadata
+│   │   ├── unit1.md             # Content units
+│   │   └── unit2.md
+│   └── sequential2/
+│       └── ...
+└── chapter2/
+    └── ...
+```
+
+**File format:** Each Markdown file can include optional YAML frontmatter for metadata:
+
+```yaml
+---
+title: My Unit Title
+order: 1
+hidden: false
+---
+
+
+```
+
+**Metadata fields:**
+- `title`: Display name (uses filename if not specified)
+- `order`: Numeric ordering (default: 9999, sorted ascending)
+- `hidden` or `draft`: Set to `true` to exclude from compilation
+- `org`, `course`, `url_name`: Available at course level for OLX metadata
+
+**Important:** Course, chapter, and sequential `index.md` files should contain only frontmatter. Any text in the body of these files will be ignored with a warning. If you need to add notes or comments for organization, use HTML comments:
+
+```markdown
+---
+title: Chapter 1
+order: 1
+---
+
+<!-- This is an internal note and will be ignored -->
+```
+
+Only unit files (non-index markdown files within sequentials) should contain actual content in their body.
+
+**Usage:**
+
+```bash
+# Compile folder markdown to single markdown
+mu /path/to/course_folder /path/to/compiled.md
+
+# Or directly to OLX
+mu /path/to/course_folder /path/to/olx/
+```
+
+**Debug mode:**
+
+To debug the folder markdown compilation process, set the `MU_DEBUG_FOLDER_MD` environment variable:
+
+```bash
+MU_DEBUG_FOLDER_MD=1 mu /path/to/course_folder /path/to/olx/
+```
+
+This will keep the temporary merged markdown file and print its location to the console, allowing you to inspect the intermediate merged markdown before it's converted to the target format.
+
 ## Examples
 
 Example courses are provided in the [examples](./examples) directory.

examples/course_folder/chapter_1/Sequential_1_1/index.md

@@ -0,0 +1,6 @@
+---
+title: Sequential 1_1
+order: 1
+---
+
+<!-- In this sequential, you will see the syllabus and solve some problems.  -->

examples/course_folder/chapter_1/Sequential_1_1/problems.md

@@ -0,0 +1,32 @@
+---
+title: Problems
+order: 3
+---
+
+
+::: {mu-type=mcq}
+
+#### Multiple choice question
+
+What is the answer to Life, the Universe, and Everything?
+
+* ✅ 6 x 7
+* ❌ 666
+* ❌ 0
+* ✅ 42
+
+:::
+
+::: {mu-type=ftq}
+
+#### Free text question
+
+How many legs does a healthy snake have?
+
+<!-- All accepted answers are listed below -->
+
+* None
+* Zero
+* 0
+
+:::