- "Double quotes" for strings (filenames, section names, CLI option arguments, etc)
- 'Single quotes' for characters and CLI option flags
- `Backticks` for keywords and identifiers (symbol names, charmap names, etc)
CLI option flags also have their leading dashes
This is an edge case of how the lexer changes behavior when
reading string literals versus reading unquoted source code.
Three double quotes would begin a multi-line string literal,
but just two are still ambiguous, so it has to `peek()` to
see whether it's inside a multi-line string literal or
outside an empty regular string.
