erusev/parsedown 1.8.0 on GitHub

The first stable release in over six years. Requires PHP 7.1+.

Breaking Changes

PHP 7.1 minimum -- dropped support for PHP 5.3, 5.4, 5.5, 5.6, and 7.0.
List separation by marker type -- lists using different markers (*, +, -, or switching between . and ) for ordered lists) are now treated as separate lists, matching the CommonMark spec.
Lazy blockquotes -- consecutive blockquotes separated by a blank line are no longer merged into one, per CommonMark.
Sparse HTML blocks -- blank lines inside block-level HTML are now wrapped in <p> tags instead of being preserved as-is.
Empty ATX headings -- # and ## on their own now produce <h1></h1> and <h2></h2> instead of being treated as paragraphs.
Extensions accessing block internals may need to update: the element structure uses element instead of text in some places (e.g. $Block['element']['element']['text'] instead of $Block['element']['text']['text']).

Regex patterns throughout the parser now use possessive quantifiers (*+, ++) to prevent catastrophic backtracking (ReDoS). This addresses denial-of-service vectors where malformed emphasis markers or other adversarial input could cause memory exhaustion or hangs.
Safe mode now sanitizes nested elements correctly via recursive AST traversal. Previously, sanitization only applied at the top level.
Extensions can mark self-produced HTML as trusted using allowRawHtmlInSafeMode so it isn't escaped in safe mode, while untrusted input remains escaped.

Setext headings now handle leading/trailing spaces correctly.
ATX heading closing # sequences are trimmed properly (e.g. # # of levels # # renders as <h1># of levels #</h1>).
Ordered lists support ) as a marker in addition to ..
Ordered lists starting with a number other than 1 no longer interrupt paragraphs.
One-column tables are now supported.
Fenced code blocks require the closing fence to have at least as many backticks/tildes as the opening fence.
HTML comments follow the CommonMark spec more closely.
Email autolinks validate against the CommonMark email definition.
Escaped tilde characters (\~\~) are no longer treated as strikethrough.

Strict mode (setStrictMode(true)) -- requires a space after # in ATX headings (CommonMark-compliant behavior).

Fixed "Uninitialized string offset" errors on certain inputs.
Fixed adjacent blockquotes being incorrectly merged.
Fixed line-break standardization when using the line() method directly.
Fixed table header validation (headers containing newlines are no longer accepted).
Fixed spaces in fenced code block class names.