ebustl_parser/

text_field.rs

//! The Text Fields (TF) of TTI blocks: the types of the decoded content, and the encoding and
//! decoding of subtitle text with control codes (Tech 3264 section 5).

use textcode::{
    Iso8859_5, Iso8859_6, Iso8859_7, Iso8859_8, decode as decode_iso8859, encode as encode_iso8859,
};

use crate::{CharacterCodeTable, latin};

/// Length of the Text Field of a TTI block
pub(crate) const TF_LENGTH: usize = 112;
/// Text Field code for CR/LF
pub(crate) const TF_CR_LF: u8 = 0x8A;
/// Text Field code for unused space, also terminating the text
pub(crate) const TF_UNUSED_SPACE: u8 = 0x8F;

// Teletext control codes, Appendix 2
const TELETEXT_END_BOX: u8 = 0x0A;
const TELETEXT_START_BOX: u8 = 0x0B;
const TELETEXT_DOUBLE_HEIGHT: u8 = 0x0D;

/// A part of the decoded Text Field of a subtitle.
///
/// Characters between control codes are combined into a single [`TextElement::Text`]. The
/// unused space code (8Fh) ends the text and is not included.
///
/// # Example
///
/// ```rust
/// use ebustl_parser::{Color, TeletextControl, TextElement};
///
/// let stl = ebustl_parser::parse_stl_from_file("stls/test.stl").unwrap();
/// assert_eq!(
///     vec![
///         TextElement::Teletext(TeletextControl::DoubleHeight),
///         TextElement::Teletext(TeletextControl::AlphaColor(Color::Cyan)),
///         TextElement::Teletext(TeletextControl::StartBox),
///         TextElement::Teletext(TeletextControl::StartBox),
///         TextElement::Text("au pied de la statue de la Liberté.".to_string()),
///         TextElement::Teletext(TeletextControl::EndBox),
///         TextElement::NewLine,
///     ],
///     stl.ttis[2].text_elements()
/// );
/// ```
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum TextElement {
    /// Characters, decoded with the Character Code Table
    Text(String),
    /// CR/LF (8Ah), starting the next row
    NewLine,
    /// A teletext control code (00h-1Fh), used for teletext subtitles. Teletext control codes
    /// occupy a character position on screen.
    Teletext(TeletextControl),
    /// A control code for open subtitles (80h-85h)
    Open(OpenControl),
    /// A code reserved for future use (86h-89h, 8Bh-8Eh and 90h-9Fh)
    Reserved(u8),
}

impl TextElement {
    /// The element for a control code, i.e. 00h-1Fh or 80h-9Fh except unused space (8Fh).
    pub(crate) fn from_control_code(code: u8) -> TextElement {
        match code {
            0x00..=0x1F => TextElement::Teletext(TeletextControl::from_code(code)),
            0x80 => TextElement::Open(OpenControl::ItalicsOn),
            0x81 => TextElement::Open(OpenControl::ItalicsOff),
            0x82 => TextElement::Open(OpenControl::UnderlineOn),
            0x83 => TextElement::Open(OpenControl::UnderlineOff),
            0x84 => TextElement::Open(OpenControl::BoxingOn),
            0x85 => TextElement::Open(OpenControl::BoxingOff),
            0x8A => TextElement::NewLine,
            code => TextElement::Reserved(code),
        }
    }
}

/// A teletext control code (00h-1Fh), Tech 3264 Appendix 2, reproduced from EBU Tech 3240.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum TeletextControl {
    /// Alphanumeric characters in the color (00h-07h)
    AlphaColor(Color),
    /// Flash (08h)
    Flash,
    /// Steady (09h)
    Steady,
    /// End box (0Ah)
    EndBox,
    /// Start box (0Bh)
    StartBox,
    /// Normal height (0Ch)
    NormalHeight,
    /// Double height (0Dh)
    DoubleHeight,
    /// Double width (0Eh)
    DoubleWidth,
    /// Double size (0Fh)
    DoubleSize,
    /// Mosaic graphics in the color (10h-17h)
    MosaicColor(Color),
    /// Conceal (18h)
    Conceal,
    /// Contiguous mosaic (19h)
    ContiguousMosaic,
    /// Separated mosaic (1Ah)
    SeparatedMosaic,
    /// Reserved (1Bh)
    Reserved,
    /// Black background (1Ch)
    BlackBackground,
    /// New background (1Dh), the background takes the current foreground color
    NewBackground,
    /// Hold mosaic (1Eh)
    HoldMosaic,
    /// Release mosaic (1Fh)
    ReleaseMosaic,
}

impl TeletextControl {
    /// The control for a code 00h-1Fh.
    fn from_code(code: u8) -> TeletextControl {
        match code {
            0x00..=0x07 => TeletextControl::AlphaColor(Color::from_code(code)),
            0x08 => TeletextControl::Flash,
            0x09 => TeletextControl::Steady,
            0x0A => TeletextControl::EndBox,
            0x0B => TeletextControl::StartBox,
            0x0C => TeletextControl::NormalHeight,
            0x0D => TeletextControl::DoubleHeight,
            0x0E => TeletextControl::DoubleWidth,
            0x0F => TeletextControl::DoubleSize,
            0x10..=0x17 => TeletextControl::MosaicColor(Color::from_code(code)),
            0x18 => TeletextControl::Conceal,
            0x19 => TeletextControl::ContiguousMosaic,
            0x1A => TeletextControl::SeparatedMosaic,
            0x1B => TeletextControl::Reserved,
            0x1C => TeletextControl::BlackBackground,
            0x1D => TeletextControl::NewBackground,
            0x1E => TeletextControl::HoldMosaic,
            _ => TeletextControl::ReleaseMosaic,
        }
    }
}

/// A teletext color, used by [`TeletextControl::AlphaColor`] and
/// [`TeletextControl::MosaicColor`].
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum Color {
    /// Black (0)
    Black,
    /// Red (1)
    Red,
    /// Green (2)
    Green,
    /// Yellow (3)
    Yellow,
    /// Blue (4)
    Blue,
    /// Magenta (5)
    Magenta,
    /// Cyan (6)
    Cyan,
    /// White (7)
    White,
}

impl Color {
    /// The color in the lowest three bits of a teletext color code.
    fn from_code(code: u8) -> Color {
        match code & 0x07 {
            0 => Color::Black,
            1 => Color::Red,
            2 => Color::Green,
            3 => Color::Yellow,
            4 => Color::Blue,
            5 => Color::Magenta,
            6 => Color::Cyan,
            _ => Color::White,
        }
    }
}

/// A control code for open (in-vision) subtitles (80h-85h).
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum OpenControl {
    /// Italics on (80h)
    ItalicsOn,
    /// Italics off (81h)
    ItalicsOff,
    /// Underline on (82h)
    UnderlineOn,
    /// Underline off (83h)
    UnderlineOff,
    /// Boxing on (84h)
    BoxingOn,
    /// Boxing off (85h)
    BoxingOff,
}

/// How the rows of a subtitle are presented
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub(crate) enum Presentation {
    /// Teletext subtitles, each row boxed and optionally in double height
    Teletext { double_height: bool },
    /// Open (in-vision) subtitles, which must not use teletext control codes
    Open,
}

impl Presentation {
    /// Control codes starting each row
    fn row_start(self) -> &'static [u8] {
        match self {
            Presentation::Teletext {
                double_height: true,
            } => &[
                TELETEXT_DOUBLE_HEIGHT,
                TELETEXT_START_BOX,
                TELETEXT_START_BOX,
            ],
            Presentation::Teletext {
                double_height: false,
            } => &[TELETEXT_START_BOX, TELETEXT_START_BOX],
            Presentation::Open => &[],
        }
    }

    /// Control codes ending each row
    fn row_end(self) -> &'static [u8] {
        match self {
            Presentation::Teletext { .. } => &[TELETEXT_END_BOX, TELETEXT_END_BOX],
            Presentation::Open => &[],
        }
    }

    /// Codes between two rows. A double height row occupies two teletext rows.
    fn row_separator(self) -> &'static [u8] {
        match self {
            Presentation::Teletext {
                double_height: true,
            } => &[TF_CR_LF, TF_CR_LF],
            _ => &[TF_CR_LF],
        }
    }
}

/// Encodes `text` into Text Fields, one per TTI block, padded with unused space (8Fh).
///
/// Rows are separated by `\n` or `\r\n`, other control characters are dropped. A character is
/// never split between two Text Fields, and the last Text Field always ends with unused space
/// as the spec requires.
pub(crate) fn encode_text_fields(
    text: &str,
    presentation: Presentation,
    cct: CharacterCodeTable,
) -> Vec<Vec<u8>> {
    let terminator = [TF_UNUSED_SPACE];
    let units = text_units(text, presentation, cct);

    let mut fields = Vec::new();
    let mut field = Vec::with_capacity(TF_LENGTH);
    for unit in units
        .iter()
        .map(Vec::as_slice)
        .chain([terminator.as_slice()])
    {
        if field.len() + unit.len() > TF_LENGTH {
            fields.push(pad(field));
            field = Vec::with_capacity(TF_LENGTH);
        }
        field.extend_from_slice(unit);
    }
    fields.push(pad(field));
    fields
}

/// Encodes `text` into a single Text Field like [`encode_text_fields`], truncating text that
/// does not fit.
pub(crate) fn encode_truncated_text_field(
    text: &str,
    presentation: Presentation,
    cct: CharacterCodeTable,
) -> Vec<u8> {
    let units = text_units(text, presentation, cct);
    // Keep at least one byte for the terminating unused space
    let mut len = 0;
    let fitting = units
        .iter()
        .take_while(|unit| {
            len += unit.len();
            len < TF_LENGTH
        })
        .count();
    pad(units[..fitting].concat())
}

/// Encodes the text as units, the bytes of a character or control code, which must be kept
/// together in one Text Field.
fn text_units(text: &str, presentation: Presentation, cct: CharacterCodeTable) -> Vec<Vec<u8>> {
    let control_codes = |codes: &[u8]| codes.iter().map(|&code| vec![code]).collect::<Vec<_>>();

    let mut units = Vec::new();
    for (i, row) in text.lines().enumerate() {
        if i > 0 {
            units.extend(control_codes(presentation.row_separator()));
        }
        units.extend(control_codes(presentation.row_start()));
        units.extend(
            row.chars()
                .filter(|c| !c.is_control())
                .map(|c| encode_characters(c.encode_utf8(&mut [0; 4]), cct)),
        );
        units.extend(control_codes(presentation.row_end()));
    }
    units
}

/// Encodes text using the given character code table.
fn encode_characters(text: &str, cct: CharacterCodeTable) -> Vec<u8> {
    match cct {
        CharacterCodeTable::Latin => latin::encode(text),
        CharacterCodeTable::LatinCyrillic => encode_iso8859::<Iso8859_5>(text),
        CharacterCodeTable::LatinArabic => encode_iso8859::<Iso8859_6>(text),
        CharacterCodeTable::LatinGreek => encode_iso8859::<Iso8859_7>(text),
        CharacterCodeTable::LatinHebrew => encode_iso8859::<Iso8859_8>(text),
    }
}

fn pad(mut field: Vec<u8>) -> Vec<u8> {
    field.resize(TF_LENGTH, TF_UNUSED_SPACE);
    field
}

/// The Text Field up to, but not including, the first unused space code (8Fh).
pub(crate) fn content(tf: &[u8]) -> &[u8] {
    let end = tf
        .iter()
        .position(|&c| c == TF_UNUSED_SPACE)
        .unwrap_or(tf.len());
    &tf[..end]
}

/// Decodes a Text Field, or several concatenated ones, into characters and control codes.
///
/// Decoding stops at the first unused space code (8Fh).
pub(crate) fn decode_elements(tf: &[u8], cct: CharacterCodeTable) -> Vec<TextElement> {
    let mut elements = Vec::new();
    // Start of the current run of character codes
    let mut run_start = 0;
    for (i, &code) in tf.iter().enumerate() {
        let is_control_code = matches!(code, 0x00..=0x1F | 0x80..=0x9F);
        if !is_control_code {
            continue;
        }
        push_text(&mut elements, &tf[run_start..i], cct);
        if code == TF_UNUSED_SPACE {
            return elements;
        }
        elements.push(TextElement::from_control_code(code));
        run_start = i + 1;
    }
    // The text may fill the field without a terminating control code
    push_text(&mut elements, &tf[run_start..], cct);
    elements
}

fn push_text(elements: &mut Vec<TextElement>, data: &[u8], cct: CharacterCodeTable) {
    if !data.is_empty() {
        elements.push(TextElement::Text(decode_characters(data, cct)));
    }
}

/// Decodes a Text Field, or several concatenated ones, into a string.
///
/// Control codes are dropped, except CR/LF which becomes `\r\n`. Decoding stops at the first
/// unused space code (8Fh).
pub(crate) fn decode(tf: &[u8], cct: CharacterCodeTable) -> String {
    let mut result = String::new();
    for element in decode_elements(tf, cct) {
        match element {
            TextElement::Text(text) => result.push_str(&text),
            TextElement::NewLine => result.push_str("\r\n"),
            _ => {}
        }
    }
    result
}

/// Decodes character codes (no control codes) using the given character code table.
fn decode_characters(data: &[u8], cct: CharacterCodeTable) -> String {
    match cct {
        CharacterCodeTable::Latin => latin::decode(data),
        CharacterCodeTable::LatinCyrillic => decode_iso8859::<Iso8859_5>(data),
        CharacterCodeTable::LatinArabic => decode_iso8859::<Iso8859_6>(data),
        CharacterCodeTable::LatinGreek => decode_iso8859::<Iso8859_7>(data),
        CharacterCodeTable::LatinHebrew => decode_iso8859::<Iso8859_8>(data),
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    const TELETEXT: Presentation = Presentation::Teletext {
        double_height: false,
    };
    const TELETEXT_DH: Presentation = Presentation::Teletext {
        double_height: true,
    };
    const LATIN: CharacterCodeTable = CharacterCodeTable::Latin;

    /// The single Text Field of `text`, without the padding
    fn encoded(text: &str, presentation: Presentation) -> Vec<u8> {
        let fields = encode_text_fields(text, presentation, LATIN);
        assert_eq!(1, fields.len());
        without_padding(&fields[0])
    }

    fn without_padding(field: &[u8]) -> Vec<u8> {
        assert_eq!(TF_LENGTH, field.len());
        let end = field.iter().position(|&c| c == TF_UNUSED_SPACE).unwrap();
        assert!(field[end..].iter().all(|&c| c == TF_UNUSED_SPACE));
        field[..end].to_vec()
    }

    #[test]
    fn teletext_row_is_boxed() {
        assert_eq!(b"\x0B\x0BHi\x0A\x0A".to_vec(), encoded("Hi", TELETEXT));
    }

    #[test]
    fn teletext_double_height_row() {
        assert_eq!(
            b"\x0D\x0B\x0BHi\x0A\x0A".to_vec(),
            encoded("Hi", TELETEXT_DH)
        );
    }

    #[test]
    fn teletext_rows_are_separated_by_cr_lf() {
        assert_eq!(
            b"\x0B\x0BOne\x0A\x0A\x8A\x0B\x0BTwo\x0A\x0A".to_vec(),
            encoded("One\nTwo", TELETEXT)
        );
    }

    #[test]
    fn teletext_double_height_rows_are_separated_by_two_cr_lf() {
        assert_eq!(
            b"\x0D\x0B\x0BOne\x0A\x0A\x8A\x8A\x0D\x0B\x0BTwo\x0A\x0A".to_vec(),
            encoded("One\nTwo", TELETEXT_DH)
        );
    }

    #[test]
    fn open_subtitle_has_no_teletext_codes() {
        assert_eq!(
            b"One\x8ATwo".to_vec(),
            encoded("One\nTwo", Presentation::Open)
        );
    }

    #[test]
    fn crlf_and_trailing_newline() {
        assert_eq!(
            b"One\x8ATwo".to_vec(),
            encoded("One\r\nTwo\n", Presentation::Open)
        );
    }

    #[test]
    fn control_characters_are_dropped() {
        assert_eq!(
            b"OneTwo".to_vec(),
            encoded("One\tTwo\r", Presentation::Open)
        );
    }

    #[test]
    fn characters_are_encoded_with_the_table() {
        assert_eq!(b"\xC2e\xA4".to_vec(), encoded("é$", Presentation::Open));
        let fields = encode_text_fields("Ж", Presentation::Open, CharacterCodeTable::LatinCyrillic);
        assert_eq!(vec![0xB6], without_padding(&fields[0]));
    }

    #[test]
    fn empty_text_is_unused_space() {
        assert_eq!(Vec::<u8>::new(), encoded("", TELETEXT));
    }

    #[test]
    fn text_filling_one_field_leaves_room_for_unused_space() {
        let fields = encode_text_fields(&"a".repeat(TF_LENGTH - 1), Presentation::Open, LATIN);
        assert_eq!(1, fields.len());
        assert_eq!(TF_UNUSED_SPACE, fields[0][TF_LENGTH - 1]);
    }

    #[test]
    fn full_field_is_followed_by_field_of_unused_space() {
        let fields = encode_text_fields(&"a".repeat(TF_LENGTH), Presentation::Open, LATIN);
        assert_eq!(2, fields.len());
        assert_eq!(vec![b'a'; TF_LENGTH], fields[0]);
        assert_eq!(vec![TF_UNUSED_SPACE; TF_LENGTH], fields[1]);
    }

    #[test]
    fn long_text_continues_in_next_fields() {
        let text = "0123456789".repeat(30);
        let fields = encode_text_fields(&text, Presentation::Open, LATIN);

        assert_eq!(3, fields.len());
        assert_eq!(text.as_bytes()[..TF_LENGTH], fields[0][..]);
        assert_eq!(text.as_bytes()[TF_LENGTH..2 * TF_LENGTH], fields[1][..]);
        assert_eq!(
            text.as_bytes()[2 * TF_LENGTH..].to_vec(),
            without_padding(&fields[2])
        );
    }

    #[test]
    fn accented_character_is_not_split_between_fields() {
        // 'é' is two bytes (C2h 65h) and would straddle the end of the first field
        let text = format!("{}é", "a".repeat(TF_LENGTH - 1));
        let fields = encode_text_fields(&text, Presentation::Open, LATIN);

        assert_eq!(2, fields.len());
        assert_eq!(vec![b'a'; TF_LENGTH - 1], without_padding(&fields[0]));
        assert_eq!(b"\xC2e".to_vec(), without_padding(&fields[1]));
    }

    #[test]
    fn truncated_field_ends_with_unused_space() {
        let field = encode_truncated_text_field(&"a".repeat(200), TELETEXT, LATIN);

        let mut expected = b"\x0B\x0B".to_vec();
        expected.extend(vec![b'a'; TF_LENGTH - 3]);
        assert_eq!(expected, without_padding(&field));
    }

    #[test]
    fn truncated_field_does_not_split_accented_character() {
        let text = format!("{}é", "a".repeat(TF_LENGTH - 2));
        let field = encode_truncated_text_field(&text, Presentation::Open, LATIN);

        assert_eq!(vec![b'a'; TF_LENGTH - 2], without_padding(&field));
    }

    #[test]
    fn short_text_is_not_truncated() {
        let field = encode_truncated_text_field("One\nTwo", TELETEXT, LATIN);
        assert_eq!(encoded("One\nTwo", TELETEXT), without_padding(&field));
    }

    #[test]
    fn content_ends_at_unused_space() {
        assert_eq!(b"One", content(b"One\x8FTwo\x8F"));
        assert_eq!(b"", content(b"\x8F\x8F"));
        assert_eq!(b"Full", content(b"Full"));
    }

    #[test]
    fn decode_drops_control_codes_except_cr_lf() {
        let tf = b"\x0D\x0B\x0BOne\x0A\x0A\x8A\x80Two\x81\x8F";
        assert_eq!("One\r\nTwo", decode(tf, LATIN));
    }

    #[test]
    fn decode_stops_at_unused_space() {
        assert_eq!("One", decode(b"One\x8FTwo", LATIN));
    }

    #[test]
    fn decode_text_without_terminating_control_code() {
        assert_eq!("a".repeat(TF_LENGTH), decode(&[b'a'; TF_LENGTH], LATIN));
    }

    #[test]
    fn decode_uses_the_table() {
        assert_eq!("é$", decode(b"\xC2e\xA4", LATIN));
        assert_eq!("Ж", decode(&[0xB6], CharacterCodeTable::LatinCyrillic));
    }

    #[test]
    fn encode_decode_roundtrip() {
        let text = "Première ligne à $5\nDeuxième ligne";
        for presentation in [TELETEXT, Presentation::Open] {
            let fields = encode_text_fields(text, presentation, LATIN);
            assert_eq!(
                "Première ligne à $5\r\nDeuxième ligne",
                decode(&fields[0], LATIN)
            );
        }
        let fields = encode_text_fields(text, TELETEXT_DH, LATIN);
        assert_eq!(
            "Première ligne à $5\r\n\r\nDeuxième ligne",
            decode(&fields[0], LATIN)
        );
    }

    #[test]
    fn decode_elements_with_control_codes() {
        let tf = b"\x0D\x06\x0B\x0BHi\x0A\x0A\x8A\x80\xC2e\x81\x86\x8Fignored";
        assert_eq!(
            vec![
                TextElement::Teletext(TeletextControl::DoubleHeight),
                TextElement::Teletext(TeletextControl::AlphaColor(Color::Cyan)),
                TextElement::Teletext(TeletextControl::StartBox),
                TextElement::Teletext(TeletextControl::StartBox),
                TextElement::Text("Hi".to_string()),
                TextElement::Teletext(TeletextControl::EndBox),
                TextElement::Teletext(TeletextControl::EndBox),
                TextElement::NewLine,
                TextElement::Open(OpenControl::ItalicsOn),
                TextElement::Text("é".to_string()),
                TextElement::Open(OpenControl::ItalicsOff),
                TextElement::Reserved(0x86),
            ],
            decode_elements(tf, LATIN)
        );
    }

    #[test]
    fn decode_elements_of_empty_field() {
        assert_eq!(
            Vec::<TextElement>::new(),
            decode_elements(&[TF_UNUSED_SPACE; TF_LENGTH], LATIN)
        );
    }

    #[test]
    fn decode_elements_of_text_filling_the_field() {
        assert_eq!(
            vec![TextElement::Text("a".repeat(TF_LENGTH))],
            decode_elements(&[b'a'; TF_LENGTH], LATIN)
        );
    }

    #[test]
    fn decode_agrees_with_decode_elements() {
        let tf = b"\x0D\x0B\x0BOne\x0A\x0A\x8A\x8A\x80Two\x81\x8F";
        assert_eq!("One\r\n\r\nTwo", decode(tf, LATIN));
    }

    #[test]
    fn teletext_control_codes() {
        use TeletextControl::*;
        let expected = [
            AlphaColor(Color::Black),
            AlphaColor(Color::Red),
            AlphaColor(Color::Green),
            AlphaColor(Color::Yellow),
            AlphaColor(Color::Blue),
            AlphaColor(Color::Magenta),
            AlphaColor(Color::Cyan),
            AlphaColor(Color::White),
            Flash,
            Steady,
            EndBox,
            StartBox,
            NormalHeight,
            DoubleHeight,
            DoubleWidth,
            DoubleSize,
            MosaicColor(Color::Black),
            MosaicColor(Color::Red),
            MosaicColor(Color::Green),
            MosaicColor(Color::Yellow),
            MosaicColor(Color::Blue),
            MosaicColor(Color::Magenta),
            MosaicColor(Color::Cyan),
            MosaicColor(Color::White),
            Conceal,
            ContiguousMosaic,
            SeparatedMosaic,
            Reserved,
            BlackBackground,
            NewBackground,
            HoldMosaic,
            ReleaseMosaic,
        ];
        for (code, control) in (0x00..=0x1F).zip(expected) {
            assert_eq!(
                TextElement::Teletext(control),
                TextElement::from_control_code(code),
                "code {code:02X}h"
            );
        }
    }

    #[test]
    fn open_subtitle_control_codes() {
        use OpenControl::*;
        let expected = [
            ItalicsOn,
            ItalicsOff,
            UnderlineOn,
            UnderlineOff,
            BoxingOn,
            BoxingOff,
        ];
        for (code, control) in (0x80..=0x85).zip(expected) {
            assert_eq!(
                TextElement::Open(control),
                TextElement::from_control_code(code),
                "code {code:02X}h"
            );
        }
    }

    #[test]
    fn cr_lf_and_reserved_codes() {
        assert_eq!(TextElement::NewLine, TextElement::from_control_code(0x8A));
        for code in (0x86..=0x89).chain(0x8B..=0x8E).chain(0x90..=0x9F) {
            assert_eq!(
                TextElement::Reserved(code),
                TextElement::from_control_code(code)
            );
        }
    }
}