Architecture

Plain has two main pieces:

• Plain, the native macOS SwiftUI app
• PlainCore, the document pipeline and reusable policy code

Page Pipeline

The pipeline is:

1. Normalize the address input.
2. Reject unsupported or unsafe URLs.
3. Fetch HTML with a privacy-oriented request policy.
4. Sanitize active and unsafe markup.
5. Extract a semantic DocumentModel.
6. Optionally fetch non-SVG images through Plain’s image pipeline.
7. Render the model with native SwiftUI/AppKit views.

Plain does not render pages through WKWebView.

URL Policy

URL normalization:

• adds https:// for domain-like inputs
• keeps supported relative URLs when there is a base URL
• turns bare search text into a Mojeek query
• strips common tracking parameters
• rejects unsupported schemes

Safety validation blocks credential-bearing URLs, localhost, private ranges, reserved ranges, and local-domain targets.

Sanitization

Plain removes scripts, styles, forms, iframes, canvas, media embeds, hidden elements, unsafe URL attributes, event handlers, and obvious tracking pixels before building the document model.

Inert JSON-LD metadata may be preserved for extraction.

Rendering

The app renders native document elements:

• headings
• paragraphs
• inline links and emphasis
• lists
• block quotes
• code blocks
• simple tables
• figures and captions
• search result cards

The output intentionally does not preserve full CSS layout. Plain rebuilds readable content, not full pages.

Local App State

Plain keeps:

• recent pages
• Later list
• reader settings
• bounded image cache
• DNS/IP resolution checks before page and image fetches

The image cache is capped at 50 MB and pruned after 30 days.