Document runnable code examples in DocBlocks

[adamziel]

Adds runnable PHP example guidance directly to the PHP Documentation Standards page. It documents the php interactive fence, // Outputs formats, and setup Blueprints used by the Code Reference.

Background

The PHP documentation standards already explain indented examples, but do not describe the opt-in syntax for examples that readers can run in WordPress Playground. This belongs with the PHP DocBlock rules, where authors already look for example guidance.

This change

• Adds a Runnable examples subsection to inline-documentation-standards/php.md, directly after Description.
• Documents the fence rules, code requirements, output forms, legacy-fence guidance, and hidden setup examples.
• Keeps the feature opt-in, so existing indented examples continue to work unchanged.
• Does not add a separate handbook page or sidebar item.

Testing

• Ran git diff --check.
• Parsed manifest.json and checked the PHP page placement, links, and Markdown fence pairs with a small validation script.

[sirreal]

https://make.wordpress.org/core/2026/09/04/runnable-code-examples-are-now-live-in-the-code-reference/