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LibWeb: Parse CSS <position>s
This parses <position> according to the following grammer: <position> = [ [ left | center | right ] || [ top | center | bottom ] | [ left | center | right | <length-percentage> ] [ top | center | bottom | <length-percentage> ]? | [ [ left | right ] <length-percentage> ] && [ [ top | bottom ] <length-percentage> ] ] The code is a little hairy and simply tries each alternative in turn, manually checking the possible orders. There may be a better way to represent this.
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MacDue
Linus Groh
parent
e568c93404
commit
ee72dcd523
2 changed files with 207 additions and 0 deletions
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@ -2518,6 +2518,212 @@ RefPtr<StyleValue> Parser::parse_linear_gradient_function(ComponentValue const&
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return LinearGradientStyleValue::create(gradient_direction, move(color_stops), gradient_type, repeating_gradient);
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}
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Optional<PositionValue> Parser::parse_position(TokenStream<ComponentValue>& tokens)
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{
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auto transaction = tokens.begin_transaction();
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tokens.skip_whitespace();
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if (!tokens.has_next_token())
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return {};
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auto parse_horizontal_preset = [&](auto ident) -> Optional<PositionValue::HorizontalPreset> {
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if (ident.equals_ignoring_case("left"sv))
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return PositionValue::HorizontalPreset::Left;
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if (ident.equals_ignoring_case("center"sv))
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return PositionValue::HorizontalPreset::Center;
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if (ident.equals_ignoring_case("right"sv))
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return PositionValue::HorizontalPreset::Right;
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return {};
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};
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auto parse_vertical_preset = [&](auto ident) -> Optional<PositionValue::VerticalPreset> {
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if (ident.equals_ignoring_case("top"sv))
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return PositionValue::VerticalPreset::Top;
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if (ident.equals_ignoring_case("center"sv))
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return PositionValue::VerticalPreset::Center;
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if (ident.equals_ignoring_case("bottom"sv))
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return PositionValue::VerticalPreset::Bottom;
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return {};
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};
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auto parse_horizontal_edge = [&](auto ident) -> Optional<PositionValue::HorizontalEdge> {
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if (ident.equals_ignoring_case("left"sv))
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return PositionValue::HorizontalEdge::Left;
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if (ident.equals_ignoring_case("right"sv))
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return PositionValue::HorizontalEdge::Right;
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return {};
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};
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auto parse_vertical_edge = [&](auto ident) -> Optional<PositionValue::VerticalEdge> {
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if (ident.equals_ignoring_case("top"sv))
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return PositionValue::VerticalEdge::Top;
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if (ident.equals_ignoring_case("bottom"sv))
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return PositionValue::VerticalEdge::Bottom;
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return {};
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};
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// <position> = [
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// [ left | center | right ] || [ top | center | bottom ]
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// |
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// [ left | center | right | <length-percentage> ]
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// [ top | center | bottom | <length-percentage> ]?
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// |
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// [ [ left | right ] <length-percentage> ] &&
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// [ [ top | bottom ] <length-percentage> ]
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// ]
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// [ left | center | right ] || [ top | center | bottom ]
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auto alternation_1 = [&]() -> Optional<PositionValue> {
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auto transaction = tokens.begin_transaction();
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PositionValue position {};
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auto& first_token = tokens.next_token();
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if (!first_token.is(Token::Type::Ident))
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return {};
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auto ident = first_token.token().ident();
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// <horizontal-position> <vertical-position>?
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auto horizontal_position = parse_horizontal_preset(ident);
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if (horizontal_position.has_value()) {
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position.horizontal_position = *horizontal_position;
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tokens.skip_whitespace();
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if (tokens.has_next_token()) {
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auto& second_token = tokens.next_token();
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if (!second_token.is(Token::Type::Ident))
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return {};
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auto vertical_position = parse_vertical_preset(second_token.token().ident());
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if (!vertical_position.has_value())
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return {};
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position.vertical_position = *vertical_position;
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}
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} else {
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// <vertical-position> <horizontal-position>?
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auto vertical_position = parse_vertical_preset(ident);
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if (!vertical_position.has_value())
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return {};
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position.vertical_position = *vertical_position;
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if (tokens.has_next_token()) {
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auto& second_token = tokens.next_token();
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if (!second_token.is(Token::Type::Ident))
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return {};
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auto horizontal_position = parse_horizontal_preset(second_token.token().ident());
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if (!horizontal_position.has_value())
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return {};
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position.horizontal_position = *horizontal_position;
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}
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}
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transaction.commit();
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return position;
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};
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// [ left | center | right | <length-percentage> ]
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// [ top | center | bottom | <length-percentage> ]?
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auto alternation_2 = [&]() -> Optional<PositionValue> {
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auto transaction = tokens.begin_transaction();
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PositionValue position {};
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auto& first_token = tokens.next_token();
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if (first_token.is(Token::Type::Ident)) {
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auto horizontal_position = parse_horizontal_preset(first_token.token().ident());
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if (!horizontal_position.has_value())
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return {};
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position.horizontal_position = *horizontal_position;
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} else {
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auto dimension = parse_dimension(first_token);
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if (!dimension.has_value() || !dimension->is_length_percentage())
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return {};
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position.horizontal_position = dimension->length_percentage();
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}
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tokens.skip_whitespace();
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if (tokens.has_next_token()) {
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auto& second_token = tokens.next_token();
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if (second_token.is(Token::Type::Ident)) {
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auto vertical_position = parse_vertical_preset(second_token.token().ident());
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if (!vertical_position.has_value())
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return {};
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position.vertical_position = *vertical_position;
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} else {
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auto dimension = parse_dimension(second_token);
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if (!dimension.has_value() || !dimension->is_length_percentage())
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return {};
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position.vertical_position = dimension->length_percentage();
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}
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}
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transaction.commit();
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return position;
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};
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// [ [ left | right ] <length-percentage> ] &&
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// [ [ top | bottom ] <length-percentage> ]
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auto alternation_3 = [&]() -> Optional<PositionValue> {
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auto transaction = tokens.begin_transaction();
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PositionValue position {};
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auto parse_horizontal = [&] {
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// [ left | right ] <length-percentage> ]
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auto transaction = tokens.begin_transaction();
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tokens.skip_whitespace();
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if (!tokens.has_next_token())
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return false;
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auto& first_token = tokens.next_token();
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if (!first_token.is(Token::Type::Ident))
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return false;
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auto horizontal_egde = parse_horizontal_edge(first_token.token().ident());
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if (!horizontal_egde.has_value())
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return false;
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position.x_relative_to = *horizontal_egde;
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tokens.skip_whitespace();
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if (!tokens.has_next_token())
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return false;
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auto& second_token = tokens.next_token();
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auto dimension = parse_dimension(second_token);
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if (!dimension.has_value() || !dimension->is_length_percentage())
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return false;
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position.horizontal_position = dimension->length_percentage();
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transaction.commit();
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return true;
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};
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auto parse_vertical = [&] {
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// [ top | bottom ] <length-percentage> ]
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auto transaction = tokens.begin_transaction();
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tokens.skip_whitespace();
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if (!tokens.has_next_token())
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return false;
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auto& first_token = tokens.next_token();
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if (!first_token.is(Token::Type::Ident))
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return false;
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auto vertical_edge = parse_vertical_edge(first_token.token().ident());
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if (!vertical_edge.has_value())
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return false;
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position.y_relative_to = *vertical_edge;
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tokens.skip_whitespace();
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if (!tokens.has_next_token())
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return false;
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auto& second_token = tokens.next_token();
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auto dimension = parse_dimension(second_token);
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if (!dimension.has_value() || !dimension->is_length_percentage())
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return false;
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position.vertical_position = dimension->length_percentage();
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transaction.commit();
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return true;
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};
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if ((parse_horizontal() && parse_vertical()) || (parse_vertical() && parse_horizontal())) {
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transaction.commit();
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return position;
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}
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return {};
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};
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// Note: The alternatives must be attempted in this order since `alternation_2' can match a prefix of `alternation_3'
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auto position = alternation_3();
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if (!position.has_value())
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position = alternation_2();
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if (!position.has_value())
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position = alternation_1();
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if (position.has_value())
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transaction.commit();
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return position;
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}
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CSSRule* Parser::convert_to_rule(NonnullRefPtr<Rule> rule)
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{
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if (rule->is_at_rule()) {
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@ -254,6 +254,7 @@ private:
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Optional<GridMinMax> parse_min_max(Vector<ComponentValue> const&);
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Optional<GridRepeat> parse_repeat(Vector<ComponentValue> const&);
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Optional<ExplicitGridTrack> parse_track_sizing_function(ComponentValue const&);
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Optional<PositionValue> parse_position(TokenStream<ComponentValue>&);
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enum class AllowedDataUrlType {
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None,
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