Saves the draft. Creates the page template on the first save (201). Saving does not change
the live page; publish the draft for that. Fields you omit keep their current value.

The draft is validated: Liquid syntax, the required top-level {% store_buttons %} tag, the
allowed HTML and CSS, the page's Content Security Policy, and the size limits (body 65,536
bytes, CSS 32,768 bytes). Problems are returned with the field and line they are on.

Saving, publishing and previewing share a limit of 60 requests per minute per API key.

Requirements: a Pro plan, page templates enabled for the project, and an API key of a project
owner or manager with the page_templates.update scope.