docs: DEV guide

Author: JesperDramsch

DEVELOPMENT.md

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+# Development Guide for Python Deadlines
+
+## Quick Development Builds
+
+The full site build with all languages and historical data can take a long time. We provide several development configurations for faster iteration:
+
+### Available Commands
+
+```bash
+# Full production build (all languages, all data) - SLOW
+pixi run serve
+
+# Development build (English + German, no archive/legacy) - FAST
+pixi run serve-dev
+
+# Minimal build (English only, minimal plugins) - FASTEST
+pixi run serve-minimal
+
+# Fast incremental build (skips initial build)
+pixi run serve-fast
+```
+
+### Build Time Comparison
+
+| Command | Languages | Archive/Legacy | Plugins | Build Time |
+|---------|-----------|----------------|---------|------------|
+| `serve` | All 9 | Yes | All | ~3-5 minutes |
+| `serve-dev` | EN, DE | No | Most | ~30-45 seconds |
+| `serve-minimal` | EN only | No | Minimal | ~15-20 seconds |
+| `serve-fast` | EN, DE | No | Most | ~10 seconds (incremental) |
+
+### Configuration Files
+
+- **`_config.yml`** - Main production configuration
+- **`_config.dev.yml`** - Development config (EN+DE, no historical data)
+- **`_config.minimal.yml`** - Minimal config (EN only, bare essentials)
+
+### How It Works
+
+Jekyll allows layering configurations using the `--config` flag:
+```bash
+jekyll serve --config _config.yml,_config.dev.yml
+```
+
+Later configs override earlier ones, so `_config.dev.yml` overrides specific settings from `_config.yml`.
+
+### What Gets Excluded in Dev Mode
+
+**Development Mode (`serve-dev`):**
+- Languages: Only English and German
+- Archive data: Not processed
+- Legacy data: Not processed
+- Some plugins: Sitemap disabled
+- Analytics: Disabled
+
+**Minimal Mode (`serve-minimal`):**
+- Languages: Only English
+- Only current conferences processed
+- Minimal plugins (no SEO, maps, sitemap)
+- All other languages excluded from file watching
+- Maximum speed optimizations
+
+### When to Use Each Mode
+
+- **`serve`** - Final testing before deployment, checking all languages
+- **`serve-dev`** - General development, testing features
+- **`serve-minimal`** - Quick iterations, CSS/JS development
+- **`serve-fast`** - Continuous development with auto-reload
+
+### Tips for Faster Development
+
+1. **Use minimal mode for CSS/JS work:**
+   ```bash
+   pixi run serve-minimal
+   ```
+
+2. **Skip link checking when sorting:**
+   ```bash
+   pixi run sort  # Uses --skip_links by default
+   ```
+
+3. **Use incremental builds:**
+   ```bash
+   pixi run serve-fast
+   ```
+
+4. **Exclude files from watch:**
+   Add large files or directories to `exclude:` in dev configs
+
+5. **Clear Jekyll cache if builds are slow:**
+   ```bash
+   rm -rf _site .jekyll-cache
+   ```
+
+### Custom Development Configuration
+
+You can create your own config for specific needs:
+
+```yaml
+# _config.custom.yml
+languages: [ "en", "es" ]  # Your preferred languages
+page_gen:
+  # Your custom page generation rules
+```
+
+Then use it:
+```bash
+bundler exec jekyll serve --config _config.yml,_config.custom.yml
+```
+
+### Troubleshooting
+
+**Build still slow?**
+- Clear cache: `rm -rf _site .jekyll-cache`
+- Check for large files in `_data/`
+- Use `--profile` flag to identify bottlenecks
+
+**Missing content in dev mode?**
+- Check which config you're using
+- Archive/legacy conferences won't appear in dev mode
+- Some languages are excluded
+
+**Changes not appearing?**
+- Restart Jekyll if you modify `_config*.yml`
+- Check if files are excluded in the config
+- Try without `--incremental` flag