/**
 * Hard linebreak (`<br />` tag).
 * - Any `\n` linebreak in a paragraph will become a hard `<br />` tag.
 * - Leading and trailing whitespace before/after the linebreak is trimmed.
 * - Different to Markdown:
 *   - Markdown needs two spaces at the end of a line to create a linebreak.
 *   - We just directly convert any `\n` linebreak into a `<br />` tag (lines without two spaces are not joined together).
 *   - This is more intuitive (a linebreak becomes a linebreak is isn't silently ignored).
 *   - This works better with textareas that wrap text (since manually breaking up long lines is no longer necessary).
 */
export declare const LINEBREAK_RULE: import("../util/rule.js").MarkupRule;