[1] Data Resource | Frictionless Standards, 2023-09-28T10:34:45.000Z, 2023-11-25T09:20:43.722Z https://specs.frictionlessdata.io/data-resource/#url-or-path

• MUST either be a URL or a POSIX path
• URLs MUST be fully qualified. MUST be using either http or https scheme. (Absence of a scheme indicates MUST be a POSIX path)
• POSIX paths (unix-style with / as separator) are supported for referencing local files, with the security restraint that they MUST be relative siblings or children of the descriptor. Absolute paths (/) and relative parent paths (…/) MUST NOT be used, and implementations SHOULD NOT support these path types.

[2] >>1 のサイトの他のいくつもの仕様書から参照されています。