htmlbag

htmlbag is the HTML/CSS renderer within the Boxes and Glue stack. It turns HTML fragments plus CSS into internal text and node structures (frontend.Text, node.VList, etc.) that are later shipped to PDF.

This project is part of a broader ecosystem of technologies for document processing, XML transformation, typesetting and PDF generation.

→ Explore its connections in Constellation

Core pieces

• CSSBuilder (cssbuilder.go): owns a frontend.Document and csshtml.CSS, parses HTML (ParseHTMLFromNode/HTMLToText), applies CSS, and builds vlists.
• Styles: inheritablestyles.go models CSS inheritance; list markers, indents, and table handling live here and in htmltable.go.
• Rendering: vlistbuilder.go builds vertical lists from frontend.Text; output.go ships pages via the frontend/pdfdraw backend.
• Fonts: fonts.go loads embedded webfonts; assets live under fonts/.

Quick start

css := csshtml.New()
_ = css.ParseString(`@page { size: A4; } body { font-family: serif; }`)
doc := frontend.NewDocument()
cb, _ := htmlbag.New(doc, css)

te, _ := cb.HTMLToText(`<p><b>Hello</b> world</p>`)
vl, _ := cb.CreateVlist(te, bag.MustSP("15cm"))
doc.Doc.OutputAt(0, 0, vl) // example: output directly

Development

• Go 1.22+. Import path: github.com/boxesandglue/htmlbag.
• Tests/lint: no test at the moment.
• Changes in the CSS/HTML pipeline should be validated against PDF references (downstream projects rely on stable output).