fix(tailwind): export STREAMDOWN_CLASSES and getSourceInline() for Tailwind v4 prefix support

[sleitor]

Problem

Fixes #450

When using Tailwind v4's prefix() option (e.g. prefix(tw)), Tailwind's build-time scanner looks for tw:flex, tw:items-center, etc. in scanned files. However, streamdown's dist files only contain the unprefixed class names (flex, items-center, etc.), so no matching CSS utilities are generated and all styling breaks.

Solution

Add a new streamdown/tailwind entry point that exports:

• STREAMDOWN_CLASSES – a readonly array of every Tailwind utility class used across streamdown and its official plugins
• getSourceInline(prefix?) – returns a ready-to-paste Tailwind v4 @source inline(...) directive with all classes, optionally prefixed

Usage with Tailwind v4 prefix

/* globals.css */
@import "tailwindcss" prefix(tw);

/* Replace 'tw' with your actual prefix: */
@source inline("tw:{absolute,animate-spin,...}");

Generate the exact directive with the helper:

// scripts/gen-streamdown-source.js
import { getSourceInline } from 'streamdown/tailwind';
process.stdout.write(getSourceInline('tw') + '\n');

node scripts/gen-streamdown-source.js >> app/globals.css

Or use the raw class array in your own tooling:

import { STREAMDOWN_CLASSES } from 'streamdown/tailwind';
// string[] – 166 Tailwind utilities used by streamdown

No-prefix usage unchanged

Users who are not using a prefix are unaffected — they continue to use @source "../node_modules/streamdown/dist/*.js" as documented.

Changes

• packages/streamdown/lib/tailwind-classes.ts – new file: exports STREAMDOWN_CLASSES and getSourceInline
• packages/streamdown/tailwind.ts – new entry point re-exporting the helpers
• packages/streamdown/tsup.config.ts – adds tailwind.ts to build entries
• packages/streamdown/package.json – adds ./tailwind export condition
• packages/streamdown/README.md – documents Tailwind v4 prefix setup
• .changeset/fix-tailwind-prefix-scanning.md – patch bump

[vercel]

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[vercel]

STREAMDOWN_CLASSES array is missing 6 Tailwind CSS utility classes ([&_thead]:sticky, [&_thead]:top-0, [&_thead]:z-10, overflow-auto, pt-0, underline) that are actively used in the source code, causing those styles to be absent when using Tailwind v4 prefix scanning.

[sleitor]

Fixed — added 20 missing utility classes that are actively used in the source but were absent from the array:

-mt-10, [&>p]:inline, [&_svg]:h-auto, [&_svg]:w-auto, [counter-increment:line_0], [counter-reset:line], [li_&]:pl-6, before:content-[counter(line)], bg-[var(--sdm-bg,inherit], bg-[var(--sdm-tbg)], border, dark:bg-[var(--shiki-dark-bg,var(--sdm-bg,inherit)], dark:bg-[var(--shiki-dark-bg,var(--sdm-tbg))], dark:text-[var(--shiki-dark,var(--sdm-c,inherit))], list-decimal, list-disc, list-inside, rounded, sticky, text-[var(--sdm-c,inherit)]

[haydenbleasel]

Thanks @sleitor but i don't think manually keeping track of all the classnames is the best way to solve, i'm hoping Tailwind have some better way of handling this 😭

[sleitor]

Thanks for the feedback, @haydenbleasel! I did dig into the Tailwind v4 docs — unfortunately there's no native mechanism to handle the prefix case with @source path scanning.

The problem: when prefix(tw) is active, Tailwind looks for tw:flex, tw:items-center etc. in scanned files. But streamdown's dist only contains unprefixed class names (flex, items-center), so @source "../node_modules/streamdown/dist/*.js" won't help here.

The Tailwind v4 docs actually recommend exactly this approach for classes that can't be picked up by static scanning — Safelisting specific utilities via @source inline().

And notably, tailwind-merge — widely used by shadcn/ui and others — takes the same approach of maintaining an explicit class list internally. It's a well-established pattern, not a fragile one.

Happy to be corrected if there's a v4 API I missed! 🙏