Function parse_with_tile_defaults 

pub fn parse_with_tile_defaults(
    tokens: Vec<Token>,
    tile_defaults: &TileOptions,
) -> Result<PolydatFile, String>

parse reading every tile that names no delimiters or sigil of its own under tile_defaults.

A tile body is raw text until it is read, and what it means depends on the delimiters it is read under, so a host that supplies its own supplies them here rather than re-reading afterwards: the text is admitted once, under the reading that was intended. A tile that names any delimiter of its own keeps all of them.