Document php as an accepted lang value for llms.txt and Markdown output

[fern-api]

Overview

Fern's /llms.txt endpoint and per-page .md/.mdx output accept a lang query parameter that filters SDK code examples to a single language, so agents consuming the docs load only the snippets they need. PHP is now an accepted lang value alongside node, python, java, ruby, go, csharp, and swift. Customers who publish a PHP SDK can now point agents and tooling at ?lang=php and get PHP-only snippets instead of every language, reducing token usage.

Implements docs for: feat(docs): support php in the lang filter for llms.txt and markdown output (fern-api/fern-platform#14851) — https://github.com/fern-api/fern-platform/pull/14851
Implements docs for: feat(docs): support php in the lang filter for llms.txt and markdown output (fern-api/fern-platform#14854, follow-up) — https://github.com/fern-api/fern-platform/pull/14854

Pages changed

• fern/products/docs/pages/ai/llms-txt/customize-llms-txt.mdx: added 'php' to the lang ParamField type union in "Filter endpoint output"; noted that lang also applies to per-page .md/.mdx URLs.
• fern/products/docs/pages/changelog/2026-09-18.mdx: new Docs changelog entry (tag ai) linking to /learn/docs/ai-features/customize-llm-output#filter-endpoint-output.

Merged main into the branch. Vale pre-commit and fern check --warnings pass on the changed files (remaining warnings are pre-existing and unrelated).

[github-actions]

🌿 Preview your docs: https://fern-preview-2026-09-16-fern-ai-1fb7a4-20eb18f4.docs.buildwithfern.com/learn

Here are the markdown pages you've updated:

• learn/docs/ai-features/customize-llm-output
• learn/docs/changelog/2026/9/18