of Markdown parsers for standardisation. However, Gruber has argued that complete standardization would be a mistake: "Different sites (and people) have different needs. No one syntax would make all happy." Gruber avoided using curly braces in Markdown to unofficially reserve them for implementation-specific extensions. Standardization From 2012, a group of people, including Jeff Atwood and John MacFarlane, launched what Atwood characterised as a standardisation effort. A community website now aims to "document various tools and resources available to document authors and developers, as well as implementors of the various Markdown implementations". In September 2014, Gruber objected to the usage of "Markdown" in the name of this effort and it was rebranded as CommonMark. CommonMark.org published several versions of a specification, reference implementation, test suite, and "[plans] to announce a finalized 1.0 spec and test suite in 2019." No 1.0 spec has since been released as major issues still remain unsolved. Nonetheless, the following websites and projects have adopted CommonMark: Discourse, GitHub, GitLab, Reddit, Qt, Stack Exchange (Stack Overflow), and Swift. In March 2016 two relevant informational Internet RFCs were published: introduced MIME type . discussed and registered the variants MultiMarkdown, GitHub Flavored Markdown (GFM), Pandoc, and Markdown Extra among others. Variants Websites like Bitbucket, Diaspora, GitHub, OpenStreetMap, Reddit, SourceForge, and Stack Exchange use variants of Markdown to facilitate discussion between users. Depending on implementation, basic inline HTML tags may be supported. Italic text may be implemented by _underscores_ and/or *single-asterisks*. GitHub Flavored Markdown GitHub had been using its own variant of Markdown since as early as 2009, adding support for additional formatting such as tables and nesting block content inside list elements, as well as GitHub-specific features such as auto-linking references to commits, issues, usernames, etc. In 2017, GitHub released a formal specification of its GitHub Flavored Markdown (GFM) that is based on CommonMark. It is a strict superset of CommonMark, following its specification exactly except for tables, strikethrough, autolinks and task lists, which GFM adds as extensions. GitHub also changed the parser used on their sites accordingly, which required that some documents be changed. For instance, GFM now requires that the hash symbol that creates a heading be separated from the heading text by a space character. Markdown Extra Markdown Extra is a lightweight markup language based on Markdown implemented in PHP (originally), Python and Ruby. It adds features not available with plain Markdown syntax. Markdown Extra is supported