InsertTextFormat

The primary text to be inserted is treated as a plain string.

The primary text to be inserted is treated as a snippet.

A snippet can define tab stops and placeholders with $1, $2 and ${3:foo}. $0 defines the final tab stop, it defaults to the end of the snippet. Placeholders with equal identifiers are linked, that is typing in one will update others too.

See also: https://microsoft.github.io/language-server-protocol/specifications/specification-current/#snippet_syntax