From @octref in #62159

This is a regression on the diagnostics display.

1.28:

Insiders:

In both case, the diagnostics returned are:

const diagnostics = {
  code: "unknownProperties",
  source: "css.lint.unknownProperties",
  message: "Unknown property: 'foo1'"
}

If we have access to semantic information we should render it much better. The message should come first. Then the source on a separate line, with a Source: label preceding it and in non-monospace font (since source should be a user-readable string like CSS Lint). Then, the code with the same style, but with monospace, since code is often a library/OS error code. Something like:

Unknown property: 'foo1'

Source: CSS Lint
Code: unknownProperties

cc @sandy081 @ramya-rao-a @misolori