Hints for elementary-theme in testing

Hints

• asv-unknown-tag
  :77 - developer
  Found invalid tag. Non-standard tags should be prefixed with `x-`. AppStream also provides the <custom/> tag to add arbitrary custom data to metainfo files. This tag is read by AppStream libraries and may be useful instead of defining new custom toplevel or `x-`-prefixed tags if you just want to add custom data to a metainfo file.
• asv-runtime-project-license-no-ref
  -
  Licenses for `runtime` components are usually too complex to reflect them in a simple SPDX expression. Consider using a `LicenseRef` and a web URL as value for this component's `project_license`. E.g. `LicenseRef-free=https://example.com/licenses.html`