syntax highlight issues for backslash inside double backquote

[tardyp]

Following snippet is valid sphinx, but produce annoying warning highlights.

It considers any of ``\r``, ``\n``, and ``\r\n`` to be newlines.
Because of the ambiguity of an append operation ending in the character ``\r`` (it may be a bare ``\r`` or half of ``\r\n``), the last line of such an append operation will be buffered until the next append or flush.

[Alhadis]

Can we please keep this confined to the one issue? The matters might be related, and having two separate issues makes feedback difficult.