//! Blank lines occur in the [flow][] content type. //! //! ## Grammar //! //! Blank lines form with the following BNF //! (see [construct][crate::construct] for character groups): //! //! ```bnf //! blank_line ::= *space_or_tab //! ``` //! //! As this construct occurs in flow, like all flow constructs, it must be //! followed by an eol (line ending) or eof (end of file). //! //! Blank lines are sometimes needed, such as to differentiate a [paragraph][] //! from a definition. //! In several cases, blank lines are not needed between flow constructs, //! such as between two [heading (atx)][heading_atx]s. //! Sometimes, whether blank lines are present, changes the behavior of how //! HTML is rendered, such as whether blank lines are present inside or between //! [list items][list_item]. //! More than one blank line is never needed in `CommonMark`. //! //! Because blank lines can be empty (line endings are not considered part of //! it), and events cannot be empty, blank lines are not present as an event. //! //! ## HTML //! //! Blank lines do not relate to an element in HTML, except for the role they //! play when inside or between [list items][list_item]. //! //! ## Recommendation //! //! It is recommended to always use a blank line between every flow construct, //! to use blank lines (consistently) between list items as desired, and to //! never use more than one blank line. //! //! ## Tokens //! //! * [`SpaceOrTab`][crate::event::Name::SpaceOrTab] //! //! ## References //! //! * [`blank-line.js` in `micromark`](https://github.com/micromark/micromark/blob/main/packages/micromark-core-commonmark/dev/lib/blank-line.js) //! * [*ยง 4.9 Blank lines* in `CommonMark`](https://spec.commonmark.org/0.30/#blank-lines) //! //! [heading_atx]: crate::construct::heading_atx //! [list_item]: crate::construct::list_item //! [paragraph]: crate::construct::paragraph //! [flow]: crate::construct::flow use crate::construct::partial_space_or_tab::space_or_tab; use crate::state::{Name as StateName, State}; use crate::tokenizer::Tokenizer; /// Start of blank line. /// /// > ๐Ÿ‘‰ **Note**: `โ ` represents a space character. /// /// ```markdown /// > | โ โ โŠ /// ^ /// > | โŠ /// ^ /// ``` pub fn start(tokenizer: &mut Tokenizer) -> State { if matches!(tokenizer.current, Some(b'\t' | b' ')) { tokenizer.attempt(State::Next(StateName::BlankLineAfter), State::Nok); State::Retry(space_or_tab(tokenizer)) } else { State::Retry(StateName::BlankLineAfter) } } /// At eof/eol, after optional whitespace. /// /// ```markdown /// > | โ โ โŠ /// ^ /// > | โŠ /// ^ /// ``` pub fn after(tokenizer: &mut Tokenizer) -> State { match tokenizer.current { None | Some(b'\n') => State::Ok, _ => State::Nok, } }