Problem: Some core syntax highlight groups are cleared with intention to
always be shown without additional highlighting. This doesn't always
work as intended, especially with fallback mechanism of @-groups.
Example: `Statement`/`Keyword` group shown in help code blocks
(`@markup.raw`) is shown as bold (from `Statement`) cyan (from
`@markup.raw`) instead of bold grey.
Solution: Explicitly use normal grey foreground in syntax groups where
it was previously implicitly assumed.
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