Export a worksheet (or range) to an HTML fragment

Cluster: xlsx-io

Scenario

A developer has read or built a workbook in memory and wants to display it in a web page without hand-writing DOM or table markup: a <table> of cell values that honors merged cells and, ideally, basic fonts, fills, borders, column widths, and number formatting. This is the inverse of authoring a cell from a markup fragment (html-fragment-to-rich-text-cell-value), where the worksheet is the source and HTML is the output.

Spec note, not a corpus case: this is an opt-in convenience feature with no failing behavior to assert yet. The durable value is the export's feature envelope and its formatting fidelity.

Desired behavior

• An opt-in export turns a worksheet, or a cell range, into an HTML fragment: at minimum a <table> of computed cell values with rowspan and colspan for merged ranges.
• A richer tier maps style facts already modeled (font weight, italic and color; fill color; borders; horizontal and vertical alignment; column widths; row heights) to inline styles or classes, and applies number-format-aware value formatting so displayed text matches the spreadsheet.
• Formulas render as their cached result, not the formula text.
• Output is a string, or streamable chunks, with no live DOM dependency, so it works server-side.

Prior art

Standalone converters and spreadsheet-viewer widgets already do value-plus-basic-style-to-table conversion and define the reasonable envelope: merged cells, basic styles, number formats. This is a display and export helper, not a layout engine.

Open questions

• Feature tiers: values-only, values plus styles, or full-fidelity? What is the default, and how is the richer tier opted into?
• Style mapping: inline styles, giving a self-contained fragment, or classes plus a supplied stylesheet, giving smaller output the caller themes?
• Number-format fidelity: reuse the same format engine that renders cells for write, so HTML and the spreadsheet agree on displayed text.
• Scope boundary: images, charts, and conditional formatting in the HTML output, or values plus static styles only?

Related: html-fragment-to-rich-text-cell-value, worksheet-model-preserves-merged-cells, set-style-over-cell-range.