//! Thematic breaks, sometimes called horizontal rules, are a construct that //! occurs in the [flow][] content type. //! //! They’re formed with the following BNF: //! //! ```bnf //! ; Restriction: all markers must be identical. //! ; Restriction: at least 3 markers must be used. //! thematic_break ::= *space_or_tab 1*(1*marker *space_or_tab) //! //! space_or_tab ::= ' ' | '\t' //! marker ::= '*' | '-' | '_' //! ``` //! //! Thematic breaks in markdown typically relate to the HTML element `
`. //! See [*§ 4.4.2 The `hr` element* in the HTML spec][html] for more info. //! //! It is recommended to use exactly three asterisks without whitespace when //! writing markdown. //! As using more than three markers has no effect other than wasting space, //! it is recommended to use exactly three markers. //! Thematic breaks formed with asterisks or dashes can interfere with //! [list][]s if there is whitespace between them: `* * *` and `- - -`. //! For these reasons, it is recommend to not use spaces or tabs between the //! markers. //! Thematic breaks formed with dashes (without whitespace) can also form //! [heading (setext)][heading_setext]. //! As dashes and underscores frequently occur in natural language and URLs, it //! is recommended to use asterisks for thematic breaks to distinguish from //! such use. //! Because asterisks can be used to form the most markdown constructs, using //! them has the added benefit of making it easier to gloss over markdown: you //! can look for asterisks to find syntax while not worrying about other //! characters. //! //! ## Tokens //! //! * [`ThematicBreak`][Token::ThematicBreak] //! * [`ThematicBreakSequence`][Token::ThematicBreakSequence] //! //! ## References //! //! * [`thematic-break.js` in `micromark`](https://github.com/micromark/micromark/blob/main/packages/micromark-core-commonmark/dev/lib/thematic-break.js) //! * [*§ 4.1 Thematic breaks* in `CommonMark`](https://spec.commonmark.org/0.30/#thematic-breaks) //! //! [flow]: crate::content::flow //! [heading_setext]: crate::construct::heading_setext //! [list]: crate::construct::list //! [html]: https://html.spec.whatwg.org/multipage/grouping-content.html#the-hr-element use super::partial_space_or_tab::{space_or_tab, space_or_tab_min_max}; use crate::constant::{TAB_SIZE, THEMATIC_BREAK_MARKER_COUNT_MIN}; use crate::state::{Name, State}; use crate::token::Token; use crate::tokenizer::Tokenizer; /// Start of a thematic break. /// /// ```markdown /// > | *** /// ^ /// ``` pub fn start(tokenizer: &mut Tokenizer) -> State { if tokenizer.parse_state.constructs.thematic_break { tokenizer.enter(Token::ThematicBreak); let name = space_or_tab_min_max( tokenizer, 0, if tokenizer.parse_state.constructs.code_indented { TAB_SIZE - 1 } else { usize::MAX }, ); tokenizer.attempt(name, State::Next(Name::ThematicBreakBefore), State::Nok) } else { State::Nok } } /// Start of a thematic break, after whitespace. /// /// ```markdown /// > | *** /// ^ /// ``` pub fn before(tokenizer: &mut Tokenizer) -> State { match tokenizer.current { Some(b'*' | b'-' | b'_') => { tokenizer.tokenize_state.marker = tokenizer.current.unwrap(); State::Retry(Name::ThematicBreakAtBreak) } _ => State::Nok, } } /// After something but before something else. /// /// ```markdown /// > | *** /// ^ /// ``` pub fn at_break(tokenizer: &mut Tokenizer) -> State { match tokenizer.current { None | Some(b'\n') if tokenizer.tokenize_state.size >= THEMATIC_BREAK_MARKER_COUNT_MIN => { tokenizer.tokenize_state.marker = 0; tokenizer.tokenize_state.size = 0; tokenizer.exit(Token::ThematicBreak); // Feel free to interrupt. tokenizer.interrupt = false; State::Ok } Some(b'*' | b'-' | b'_') if tokenizer.current.unwrap() == tokenizer.tokenize_state.marker => { tokenizer.enter(Token::ThematicBreakSequence); State::Retry(Name::ThematicBreakSequence) } _ => { tokenizer.tokenize_state.marker = 0; tokenizer.tokenize_state.size = 0; State::Nok } } } /// In a sequence of markers. /// /// ```markdown /// > | *** /// ^ /// ``` pub fn sequence(tokenizer: &mut Tokenizer) -> State { match tokenizer.current { Some(b'*' | b'-' | b'_') if tokenizer.current.unwrap() == tokenizer.tokenize_state.marker => { tokenizer.consume(); tokenizer.tokenize_state.size += 1; State::Next(Name::ThematicBreakSequence) } _ => { tokenizer.exit(Token::ThematicBreakSequence); let name = space_or_tab(tokenizer); tokenizer.attempt( name, State::Next(Name::ThematicBreakAtBreak), State::Next(Name::ThematicBreakAtBreak), ) } } }