Learn when SwiftSyntax exposes declaration annotated as @_spi.
Functions marked as @_spi(RawSyntax) (where RawSyntax can be any name) are considered SPI (System Programming Interface) and are only accessible if the module that declares them is imported as @_spi(RawSyntax).
Since functions marked as SPI are not part of the public API, swift-syntax makes no guarantee to their source stability. swift-syntax makes no effort to keep its SPI stable.
Declarations are typically marked as SPI because they have some kind of caveat that makes them unsafe to use in general. For example, when accessing RawSyntax nodes, you need to manually guarantee that the SyntaxArena they’re allocated in will not be de-allocated. Other declarations have an @_spi to share them between different modules within the swift-syntax package. These would use the package modifier if not for the fact that swift-syntax needed to compile with the last two Swift releases (see doc:Swift-Version).