• b : sub::Colour
• back_colour : Style
• bold : sub::Block , sub::RawSubtitle
• font_size : Style , sub::Block , sub::RawSubtitle
• from : sub::RawSubtitle , sub::Subtitle
• g : sub::Colour
• italic : sub::Block , sub::RawSubtitle
• line : sub::VerticalPosition
• lines : sub::VerticalPosition
• proportional : sub::HorizontalPosition , sub::VerticalPosition
• r : sub::Colour
• reference : sub::VerticalPosition
• text : sub::Block , sub::RawSubtitle
• to : sub::RawSubtitle , sub::Subtitle
• underline : sub::Block , sub::RawSubtitle
• vertical_position : sub::Line , sub::RawSubtitle