What are pound directives, attribute IDs, object literals, and placeholders?

    "source.lang.swift.syntaxtype.pounddirective.keyword"
    
    "source.lang.swift.syntaxtype.attribute.id"
    
    "source.lang.swift.syntaxtype.placeholder"
    "source.lang.swift.syntaxtype.objectliteral"

what are these syntaxmap species? I thought pound directives were things like #keyPath and _ was the placeholder, but those are all apparently keywords.

pounddirective.keyword are #error/#warning/#sourceLocation.

attribute.id - for syntax highlight treat like attribute.builtin, in practice I think a known decl attribute in the wrong place or a known type attribute (there are oddities in the syntax map here, check it out for @escaping).

placeholder is for Xcode placeholder strings from eg. auto completion (and fixits?)

objectliteral is #colorLiteral and friends.

See syntax model header & implementation.